Load locales from text files

4 files changed, 379 insertions, 331 deletions

diff --git a/src/main/java/sevenUnitsGUI/Presenter.java b/src/main/java/sevenUnitsGUI/Presenter.java
index 21f2951..1cbac47 100644
--- a/src/main/java/sevenUnitsGUI/Presenter.java
+++ b/src/main/java/sevenUnitsGUI/Presenter.java
@@ -16,7 +16,6 @@
  */
 package sevenUnitsGUI;
 
-import java.io.BufferedWriter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Files;
@@ -58,7 +57,7 @@ import sevenUnitsGUI.StandardDisplayRules.UncertaintyBased;
 
 /**
  * An object that handles interactions between the view and the backend code
- * 
+ *
  * @author Adrien Hopkins
  * @since 2021-12-15
  */
@@ -78,19 +77,23 @@ public final class Presenter {
 	/** A Predicate that returns true iff the argument is a full base unit */
 	private static final Predicate<Unit> IS_FULL_BASE = unit -> unit instanceof LinearUnit
 			&& ((LinearUnit) unit).isBase();
-	/** 
+	/**
 	 * The default locale, used in two situations:
 	 * <ul>
-	 * <li> If no text is available in your locale,
-	 * uses text from this locale.
-	 * <li> Users are initialized with this locale.
+	 * <li>If no text is available in your locale, uses text from this locale.
+	 * <li>Users are initialized with this locale.
 	 * </ul>
 	 */
-	static final String DEFAULT_LOCALE = "en";
-	
+	static final String DEFAULT_LOCALE = "eo";
+
+	private static final List<String> LOCAL_LOCALES = List.of("en", "fr");
+	private static final Path USER_LOCALES_DIR = userConfigDir()
+			.resolve("SevenUnits").resolve("locales");
+
+
 	/**
 	 * Adds default units and dimensions to a database.
-	 * 
+	 *
 	 * @param database database to add to
 	 * @since 2019-04-14
 	 * @since v0.2.0
@@ -109,20 +112,20 @@ public final class Presenter {
 		// nonlinear units - must be loaded manually
 		database.addUnit("tempCelsius", Metric.CELSIUS);
 		database.addUnit("tempFahrenheit", BritishImperial.FAHRENHEIT);
-		
+
 		// load initial dimensions
 		database.addDimension("Length", Metric.Dimensions.LENGTH);
 		database.addDimension("Mass", Metric.Dimensions.MASS);
 		database.addDimension("Time", Metric.Dimensions.TIME);
 		database.addDimension("Temperature", Metric.Dimensions.TEMPERATURE);
 	}
-	
+
 	private static String displayRuleToString(
 			Function<UncertainDouble, String> numberDisplayRule) {
 		if (numberDisplayRule instanceof FixedDecimals)
 			return String.format("FIXED_DECIMALS %d",
 					((FixedDecimals) numberDisplayRule).decimalPlaces());
-		else if (numberDisplayRule instanceof FixedPrecision)
+		if (numberDisplayRule instanceof FixedPrecision)
 			return String.format("FIXED_PRECISION %d",
 					((FixedPrecision) numberDisplayRule).significantFigures());
 		else if (numberDisplayRule instanceof UncertaintyBased)
@@ -130,21 +133,21 @@ public final class Presenter {
 		else
 			return numberDisplayRule.toString();
 	}
-	
+
 	/**
 	 * Determines where to wrap {@code toWrap} with a max line length of
 	 * {@code maxLineLength}. If no good spot is found, returns -1.
 	 *
 	 * @since 2024-08-22
 	 */
-	private static final int findLineSplit(String toWrap, int maxLineLength) {
-		for (int i = maxLineLength - 1; i >= 0; i--) {
+	private static int findLineSplit(String toWrap, int maxLineLength) {
+		for (var i = maxLineLength - 1; i >= 0; i--) {
 			if (Character.isWhitespace(toWrap.charAt(i)))
 				return i;
 		}
 		return -1;
 	}
-	
+
 	/**
 	 * Gets the text of a resource file as a set of strings (each one is one line
 	 * of the text).
@@ -153,11 +156,11 @@ public final class Presenter {
 	 * @return contents of file
 	 * @since 2021-03-27
 	 */
-	private static final List<String> getLinesFromResource(String filename) {
+	private static List<String> getLinesFromResource(String filename) {
 		final List<String> lines = new ArrayList<>();
-		
-		try (InputStream stream = inputStream(filename);
-				Scanner scanner = new Scanner(stream)) {
+
+		try (var stream = inputStream(filename);
+				var scanner = new Scanner(stream)) {
 			while (scanner.hasNextLine()) {
 				lines.add(scanner.nextLine());
 			}
@@ -165,10 +168,10 @@ public final class Presenter {
 			throw new AssertionError(
 					"Error occurred while loading file " + filename, e);
 		}
-		
+
 		return lines;
 	}
-	
+
 	/**
 	 * Gets an input stream for a resource file.
 	 *
@@ -176,98 +179,97 @@ public final class Presenter {
 	 * @return obtained Path
 	 * @since 2021-03-27
 	 */
-	private static final InputStream inputStream(String filepath) {
+	private static InputStream inputStream(String filepath) {
 		return Presenter.class.getResourceAsStream(filepath);
 	}
-	
+
 	/**
 	 * Convert a linear unit value to a string, where the number is rounded to
 	 * the nearest integer.
 	 *
 	 * @since 2024-08-16
 	 */
-	private static final String linearUnitValueIntToString(LinearUnitValue uv) {
+	private static String linearUnitValueIntToString(LinearUnitValue uv) {
 		return Long.toString(Math.round(uv.getValueExact())) + " " + uv.getUnit();
 	}
-	
+
 	private static Map.Entry<String, String> parseSettingLine(String line) {
-		final int equalsIndex = line.indexOf('=');
+		final var equalsIndex = line.indexOf('=');
 		if (equalsIndex == -1)
 			throw new IllegalStateException(
 					"Settings file is malformed at line: " + line);
-		
-		final String param = line.substring(0, equalsIndex);
-		final String value = line.substring(equalsIndex + 1);
-		
+
+		final var param = line.substring(0, equalsIndex);
+		final var value = line.substring(equalsIndex + 1);
+
 		return Map.entry(param, value);
 	}
-	
+
 	/** Gets a Path from a pathname in the config file. */
 	private static Path pathFromConfig(String pathname) {
 		return CONFIG_FILE.getParent().resolve(pathname);
 	}
-	
+
 	// ====== SETTINGS ======
-	
+
 	private static String searchRuleToString(
 			Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> searchRule) {
 		if (PrefixSearchRule.NO_PREFIXES.equals(searchRule))
 			return "NO_PREFIXES";
-		else if (PrefixSearchRule.COMMON_PREFIXES.equals(searchRule))
+		if (PrefixSearchRule.COMMON_PREFIXES.equals(searchRule))
 			return "COMMON_PREFIXES";
 		else if (PrefixSearchRule.ALL_METRIC_PREFIXES.equals(searchRule))
 			return "ALL_METRIC_PREFIXES";
 		else
 			return searchRule.toString();
 	}
-	
+
 	/**
 	 * @return true iff a and b have any elements in common
 	 * @since 2022-04-19
 	 */
-	private static final boolean sharesAnyElements(Set<?> a, Set<?> b) {
+	private static boolean sharesAnyElements(Set<?> a, Set<?> b) {
 		for (final Object e : a) {
 			if (b.contains(e))
 				return true;
 		}
 		return false;
 	}
-	
-	private static final Path userConfigDir() {
+
+	private static Path userConfigDir() {
 		if (System.getProperty("os.name").startsWith("Windows")) {
-			final String envFolder = System.getenv("LOCALAPPDATA");
+			final var envFolder = System.getenv("LOCALAPPDATA");
 			if (envFolder == null || "".equals(envFolder))
 				return Path.of(System.getenv("USERPROFILE"), "AppData", "Local");
 			else
 				return Path.of(envFolder);
-		} else {
-			final String envFolder = System.getenv("XDG_CONFIG_HOME");
-			if (envFolder == null || "".equals(envFolder))
-				return Path.of(System.getenv("HOME"), ".config");
-			else
-				return Path.of(envFolder);
 		}
+		final var envFolder = System.getenv("XDG_CONFIG_HOME");
+		if (envFolder == null || "".equals(envFolder))
+			return Path.of(System.getenv("HOME"), ".config");
+		else
+			return Path.of(envFolder);
 	}
-	
+
 	/**
 	 * @return {@code line} with any comments removed.
 	 * @since 2021-03-13
 	 */
-	private static final String withoutComments(String line) {
-		final int index = line.indexOf('#');
+	private static String withoutComments(String line) {
+		final var index = line.indexOf('#');
 		return index == -1 ? line : line.substring(0, index);
 	}
-	
+
 	/**
 	 * Wraps a string, ensuring no line is longer than {@code maxLineLength}.
-	 * 
+	 *
 	 * @since 2024-08-22
 	 */
-	private static final String wrapString(String toWrap, int maxLineLength) {
-		final StringBuilder wrapped = new StringBuilder(toWrap.length());
-		String remaining = toWrap;
+	private static String wrapString(String toWrap, int maxLineLength) {
+		final var wrapped = new StringBuilder(toWrap.length());
+		var remaining = toWrap;
 		while (remaining.length() > maxLineLength) {
-			final int spot = findLineSplit(toWrap, maxLineLength);
+			final var spot = findLineSplit(toWrap, maxLineLength);
 			if (spot == -1) {
 				wrapped.append(remaining.substring(0, maxLineLength));
 				wrapped.append("-\n");
@@ -281,23 +283,23 @@ public final class Presenter {
 		wrapped.append(remaining);
 		return wrapped.toString();
 	}
-	
+
 	/**
 	 * The view that this presenter communicates with
 	 */
 	private final View view;
-	
+
 	/**
 	 * The database that this presenter communicates with (effectively the model)
 	 */
 	final UnitDatabase database;
-	
+
 	/**
 	 * The rule used for parsing input numbers. Any number-string inputted into
 	 * this program will be parsed using this method. <b>Not implemented yet.</b>
 	 */
 	private Function<String, UncertainDouble> numberParsingRule;
-	
+
 	/**
 	 * The rule used for displaying the results of unit conversions. The result
 	 * of unit conversions will be put into this function, and the resulting
@@ -305,50 +307,50 @@ public final class Presenter {
 	 */
 	private Function<UncertainDouble, String> numberDisplayRule = StandardDisplayRules
 			.uncertaintyBased();
-	
+
 	/**
 	 * A predicate that determines whether or not a certain combination of
 	 * prefixes is allowed. If it returns false, a combination of prefixes will
 	 * not be allowed. Prefixes are put in the list from right to left.
 	 */
 	private Predicate<List<UnitPrefix>> prefixRepetitionRule = DefaultPrefixRepetitionRule.NO_RESTRICTION;
-	
+
 	/**
 	 * A rule that accepts a prefixless name-unit pair and returns a map mapping
 	 * names to prefixed versions of that unit (including the unit itself) that
 	 * should be searchable.
 	 */
 	private Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> searchRule = PrefixSearchRule.NO_PREFIXES;
-	
+
 	/**
 	 * The set of units that is considered neither metric nor nonmetric for the
 	 * purposes of the metric-imperial one-way conversion. These units are
 	 * included in both From and To, even if One Way Conversion is enabled.
 	 */
 	private final Set<String> metricExceptions;
-	
+
 	/** maps locale names (e.g. 'en') to key-text maps */
 	final Map<String, Map<String, String>> locales;
-	
+
 	/** name of locale in locales to use */
 	String userLocale;
-	
+
 	/**
 	 * If this is true, views that show units as a list will have metric units
 	 * removed from the From unit list and imperial/USC units removed from the To
 	 * unit list.
 	 */
 	private boolean oneWayConversionEnabled = false;
-	
+
 	/**
 	 * If this is false, duplicate units and prefixes will be removed from the
 	 * unit view in views that show units as a list to choose from.
 	 */
 	private boolean showDuplicates = false;
-	
+
 	/**
 	 * Creates a Presenter
-	 * 
+	 *
 	 * @param view the view that this presenter communicates with
 	 * @since 2021-12-15
 	 */
@@ -356,30 +358,30 @@ public final class Presenter {
 		this.view = view;
 		this.database = new UnitDatabase();
 		addDefaults(this.database);
-		
+
 		// load units and prefixes
-		try (final InputStream units = inputStream(DEFAULT_UNITS_FILEPATH)) {
+		try (final var units = inputStream(DEFAULT_UNITS_FILEPATH)) {
 			this.handleLoadErrors(this.database.loadUnitsFromStream(units));
 		} catch (final IOException e) {
 			throw new AssertionError("Loading of unitsfile.txt failed.", e);
 		}
-		
+
 		// load dimensions
-		try (final InputStream dimensions = inputStream(
+		try (final var dimensions = inputStream(
 				DEFAULT_DIMENSIONS_FILEPATH)) {
 			this.handleLoadErrors(
 					this.database.loadDimensionsFromStream(dimensions));
 		} catch (final IOException e) {
 			throw new AssertionError("Loading of dimensionfile.txt failed.", e);
 		}
-		
+
 		// load metric exceptions
 		try {
 			this.metricExceptions = new HashSet<>();
-			try (InputStream exceptions = inputStream(DEFAULT_EXCEPTIONS_FILEPATH);
-					Scanner scanner = new Scanner(exceptions)) {
+			try (var exceptions = inputStream(DEFAULT_EXCEPTIONS_FILEPATH);
+					var scanner = new Scanner(exceptions)) {
 				while (scanner.hasNextLine()) {
-					final String line = Presenter
+					final var line = Presenter
 							.withoutComments(scanner.nextLine());
 					if (!line.isBlank()) {
 						this.metricExceptions.add(line);
@@ -390,19 +392,19 @@ public final class Presenter {
 			throw new AssertionError("Loading of metric_exceptions.txt failed.",
 					e);
 		}
-		
-		// TODO load locales
-		this.locales = new HashMap<>();
-		
+
+		this.locales = this.loadLocales();
+		this.userLocale = DEFAULT_LOCALE;
+
 		// set default settings temporarily
 		if (Files.exists(CONFIG_FILE)) {
 			this.loadSettings(CONFIG_FILE);
 		}
-		
+
 		// print out unit counts
 		System.out.println(this.loadStatMsg());
 	}
-	
+
 	/**
 	 * Applies a search rule to an entry in a name-unit map.
 	 *
@@ -410,23 +412,23 @@ public final class Presenter {
 	 * @return stream of entries, ready for flat-mapping
 	 * @since 2022-07-06
 	 */
-	private final Stream<Map.Entry<String, Unit>> applySearchRule(
+	private Stream<Map.Entry<String, Unit>> applySearchRule(
 			Map.Entry<String, Unit> e) {
-		final Unit u = e.getValue();
+		final var u = e.getValue();
 		if (u instanceof LinearUnit) {
-			final String name = e.getKey();
+			final var name = e.getKey();
 			final Map.Entry<String, LinearUnit> linearEntry = Map.entry(name,
 					(LinearUnit) u);
 			return this.searchRule.apply(linearEntry).entrySet().stream().map(
 					entry -> Map.entry(entry.getKey(), (Unit) entry.getValue()));
-		} else
-			return Stream.of(e);
+		}
+		return Stream.of(e);
 	}
-	
+
 	/**
 	 * Converts from the view's input expression to its output expression.
 	 * Displays an error message if any of the required fields are invalid.
-	 * 
+	 *
 	 * @throws UnsupportedOperationException if the view does not support
 	 *                                       expression-based conversion (does
 	 *                                       not implement
@@ -434,49 +436,46 @@ public final class Presenter {
 	 * @since 2021-12-15
 	 */
 	public void convertExpressions() {
-		if (this.view instanceof ExpressionConversionView) {
-			final ExpressionConversionView xcview = (ExpressionConversionView) this.view;
-			
-			final String fromExpression = xcview.getFromExpression();
-			final String toExpression = xcview.getToExpression();
-			
-			// expressions must not be empty
-			if (fromExpression.isEmpty()) {
-				this.view.showErrorMessage("Parse Error",
-						"Please enter a unit expression in the From: box.");
-				return;
-			}
-			if (toExpression.isEmpty()) {
-				this.view.showErrorMessage("Parse Error",
-						"Please enter a unit expression in the To: box.");
-				return;
-			}
-			
-			final Optional<UnitConversionRecord> uc;
-			if (this.database.containsUnitSetName(toExpression)) {
-				uc = this.convertExpressionToNamedMultiUnit(fromExpression,
-						toExpression);
-			} else if (toExpression.contains(";")) {
-				final String[] toExpressions = toExpression.split(";");
-				uc = this.convertExpressionToMultiUnit(fromExpression,
-						toExpressions);
-			} else {
-				uc = this.convertExpressionToExpression(fromExpression,
-						toExpression);
-			}
-			
-			uc.ifPresent(xcview::showExpressionConversionOutput);
-		} else
+		if (!(this.view instanceof ExpressionConversionView))
 			throw new UnsupportedOperationException(
 					"This function can only be called when the view is an ExpressionConversionView");
+		final var xcview = (ExpressionConversionView) this.view;
+
+		final var fromExpression = xcview.getFromExpression();
+		final var toExpression = xcview.getToExpression();
+
+		// expressions must not be empty
+		if (fromExpression.isEmpty()) {
+			this.view.showErrorMessage("Parse Error",
+					"Please enter a unit expression in the From: box.");
+			return;
+		}
+		if (toExpression.isEmpty()) {
+			this.view.showErrorMessage("Parse Error",
+					"Please enter a unit expression in the To: box.");
+			return;
+		}
+
+		final Optional<UnitConversionRecord> uc;
+		if (this.database.containsUnitSetName(toExpression)) {
+			uc = this.convertExpressionToNamedMultiUnit(fromExpression,
+					toExpression);
+		} else if (toExpression.contains(";")) {
+			final var toExpressions = toExpression.split(";");
+			uc = this.convertExpressionToMultiUnit(fromExpression, toExpressions);
+		} else {
+			uc = this.convertExpressionToExpression(fromExpression, toExpression);
+		}
+
+		uc.ifPresent(xcview::showExpressionConversionOutput);
 	}
-	
+
 	/**
 	 * Converts a unit expression to another expression.
-	 * 
+	 *
 	 * If an error happened, it is shown to the view and Optional.empty() is
 	 * returned.
-	 * 
+	 *
 	 * @since 2024-08-15
 	 */
 	private Optional<UnitConversionRecord> convertExpressionToExpression(
@@ -498,34 +497,33 @@ public final class Presenter {
 					"Could not recognize text in To entry: " + e.getMessage());
 			return Optional.empty();
 		}
-		
+
 		// convert and show output
-		if (from.getUnit().canConvertTo(to)) {
-			final UncertainDouble uncertainValue;
-			
-			// uncertainty is meaningless for non-linear units, so we will have
-			// to erase uncertainty information for them
-			if (to instanceof LinearUnit) {
-				final var toLinear = (LinearUnit) to;
-				uncertainValue = from.convertTo(toLinear).getValue();
-			} else {
-				final double value = from.asUnitValue().convertTo(to).getValue();
-				uncertainValue = UncertainDouble.of(value, 0);
-			}
-			
-			final UnitConversionRecord uc = UnitConversionRecord.valueOf(
-					fromExpression, toExpression, "",
-					this.numberDisplayRule.apply(uncertainValue));
-			return Optional.of(uc);
-		} else {
+		if (!from.getUnit().canConvertTo(to)) {
 			this.view.showErrorMessage("Conversion Error",
 					"Cannot convert between \"" + fromExpression + "\" and \""
 							+ toExpression + "\".");
 			return Optional.empty();
 		}
-		
+		final UncertainDouble uncertainValue;
+
+		// uncertainty is meaningless for non-linear units, so we will have
+		// to erase uncertainty information for them
+		if (to instanceof LinearUnit) {
+			final var toLinear = (LinearUnit) to;
+			uncertainValue = from.convertTo(toLinear).getValue();
+		} else {
+			final var value = from.asUnitValue().convertTo(to).getValue();
+			uncertainValue = UncertainDouble.of(value, 0);
+		}
+
+		final var uc = UnitConversionRecord.valueOf(
+				fromExpression, toExpression, "",
+				this.numberDisplayRule.apply(uncertainValue));
+		return Optional.of(uc);
+
 	}
-	
+
 	/**
 	 * Convert an expression to a MultiUnit. If an error happened, it is shown to
 	 * the view and Optional.empty() is returned.
@@ -542,27 +540,26 @@ public final class Presenter {
 					"Could not recognize text in From entry: " + e.getMessage());
 			return Optional.empty();
 		}
-		
+
 		final List<LinearUnit> toUnits = new ArrayList<>(toExpressions.length);
-		for (int i = 0; i < toExpressions.length; i++) {
+		for (final String toExpression : toExpressions) {
 			try {
-				final Unit toI = this.database
-						.getUnitFromExpression(toExpressions[i].trim());
-				if (toI instanceof LinearUnit) {
-					toUnits.add((LinearUnit) toI);
-				} else {
+				final var toI = this.database
+						.getUnitFromExpression(toExpression.trim());
+				if (!(toI instanceof LinearUnit)) {
 					this.view.showErrorMessage("Unit Type Error",
 							"Units separated by ';' must be linear; " + toI
 									+ " is not.");
 					return Optional.empty();
 				}
+				toUnits.add((LinearUnit) toI);
 			} catch (final IllegalArgumentException | NoSuchElementException e) {
 				this.view.showErrorMessage("Parse Error",
 						"Could not recognize text in To entry: " + e.getMessage());
 				return Optional.empty();
 			}
 		}
-		
+
 		final List<LinearUnitValue> toValues;
 		try {
 			toValues = from.convertToMultiple(toUnits);
@@ -571,12 +568,12 @@ public final class Presenter {
 					"Invalid units separated by ';': " + e.getMessage());
 			return Optional.empty();
 		}
-		
-		final String toExpression = this.linearUnitValueSumToString(toValues);
+
+		final var toExpression = this.linearUnitValueSumToString(toValues);
 		return Optional.of(
 				UnitConversionRecord.valueOf(fromExpression, toExpression, "", ""));
 	}
-	
+
 	/**
 	 * Convert an expression to a MultiUnit with a name from the database. If an
 	 * error happened, it is shown to the view and Optional.empty() is returned.
@@ -593,8 +590,8 @@ public final class Presenter {
 					"Could not recognize text in From entry: " + e.getMessage());
 			return Optional.empty();
 		}
-		
-		final List<LinearUnit> toUnits = this.database.getUnitSet(toName);
+
+		final var toUnits = this.database.getUnitSet(toName);
 		final List<LinearUnitValue> toValues;
 		try {
 			toValues = from.convertToMultiple(toUnits);
@@ -603,16 +600,16 @@ public final class Presenter {
 					"Invalid units separated by ';': " + e.getMessage());
 			return Optional.empty();
 		}
-		
-		final String toExpression = this.linearUnitValueSumToString(toValues);
+
+		final var toExpression = this.linearUnitValueSumToString(toValues);
 		return Optional.of(
 				UnitConversionRecord.valueOf(fromExpression, toExpression, "", ""));
 	}
-	
+
 	/**
 	 * Converts from the view's input unit to its output unit. Displays an error
 	 * message if any of the required fields are invalid.
-	 * 
+	 *
 	 * @throws UnsupportedOperationException if the view does not support
 	 *                                       unit-based conversion (does not
 	 *                                       implement
@@ -620,64 +617,61 @@ public final class Presenter {
 	 * @since 2021-12-15
 	 */
 	public void convertUnits() {
-		if (this.view instanceof UnitConversionView) {
-			final UnitConversionView ucview = (UnitConversionView) this.view;
-			
-			final Optional<String> fromUnitOptional = ucview.getFromSelection();
-			final Optional<String> toUnitOptional = ucview.getToSelection();
-			final String inputValueString = ucview.getInputValue();
-			
-			// extract values from optionals
-			final String fromUnitString, toUnitString;
-			if (fromUnitOptional.isPresent()) {
-				fromUnitString = fromUnitOptional.orElseThrow();
-			} else {
-				this.view.showErrorMessage("Unit Selection Error",
-						"Please specify a From unit");
-				return;
-			}
-			if (toUnitOptional.isPresent()) {
-				toUnitString = toUnitOptional.orElseThrow();
-			} else {
-				this.view.showErrorMessage("Unit Selection Error",
-						"Please specify a To unit");
-				return;
-			}
-			
-			// convert strings to data, checking if anything is invalid
-			final Unit fromUnit;
-			final UncertainDouble uncertainValue;
-			
-			if (this.database.containsUnitName(fromUnitString)) {
-				fromUnit = this.database.getUnit(fromUnitString);
-			} else
-				throw this.viewError("Nonexistent From unit: %s", fromUnitString);
-			try {
-				uncertainValue = UncertainDouble
-						.fromRoundedString(inputValueString);
-			} catch (final NumberFormatException e) {
-				this.view.showErrorMessage("Value Error",
-						"Invalid value " + inputValueString);
-				return;
-			}
-			if (this.database.containsUnitName(toUnitString)) {
-				final Unit toUnit = this.database.getUnit(toUnitString);
-				ucview.showUnitConversionOutput(
-						this.convertUnitToUnit(fromUnitString, toUnitString,
-								inputValueString, fromUnit, toUnit, uncertainValue));
-			} else if (this.database.containsUnitSetName(toUnitString)) {
-				final List<LinearUnit> toMulti = this.database
-						.getUnitSet(toUnitString);
-				ucview.showUnitConversionOutput(
-						this.convertUnitToMulti(fromUnitString, inputValueString,
-								fromUnit, toMulti, uncertainValue));
-			} else
-				throw this.viewError("Nonexistent To unit: %s", toUnitString);
-		} else
+		if (!(this.view instanceof UnitConversionView))
 			throw new UnsupportedOperationException(
 					"This function can only be called when the view is a UnitConversionView.");
+		final var ucview = (UnitConversionView) this.view;
+
+		final var fromUnitOptional = ucview.getFromSelection();
+		final var toUnitOptional = ucview.getToSelection();
+		final var inputValueString = ucview.getInputValue();
+
+		// extract values from optionals
+		final String fromUnitString, toUnitString;
+		if (fromUnitOptional.isPresent()) {
+			fromUnitString = fromUnitOptional.orElseThrow();
+		} else {
+			this.view.showErrorMessage("Unit Selection Error",
+					"Please specify a From unit");
+			return;
+		}
+		if (toUnitOptional.isPresent()) {
+			toUnitString = toUnitOptional.orElseThrow();
+		} else {
+			this.view.showErrorMessage("Unit Selection Error",
+					"Please specify a To unit");
+			return;
+		}
+
+		// convert strings to data, checking if anything is invalid
+		final Unit fromUnit;
+		final UncertainDouble uncertainValue;
+
+		if (this.database.containsUnitName(fromUnitString)) {
+			fromUnit = this.database.getUnit(fromUnitString);
+		} else
+			throw this.viewError("Nonexistent From unit: %s", fromUnitString);
+		try {
+			uncertainValue = UncertainDouble.fromRoundedString(inputValueString);
+		} catch (final NumberFormatException e) {
+			this.view.showErrorMessage("Value Error",
+					"Invalid value " + inputValueString);
+			return;
+		}
+		if (this.database.containsUnitName(toUnitString)) {
+			final var toUnit = this.database.getUnit(toUnitString);
+			ucview.showUnitConversionOutput(
+					this.convertUnitToUnit(fromUnitString, toUnitString,
+							inputValueString, fromUnit, toUnit, uncertainValue));
+		} else if (this.database.containsUnitSetName(toUnitString)) {
+			final var toMulti = this.database
+					.getUnitSet(toUnitString);
+			ucview.showUnitConversionOutput(this.convertUnitToMulti(fromUnitString,
+					inputValueString, fromUnit, toMulti, uncertainValue));
+		} else
+			throw this.viewError("Nonexistent To unit: %s", toUnitString);
 	}
-	
+
 	private UnitConversionRecord convertUnitToMulti(String fromUnitString,
 			String inputValueString, Unit fromUnit, List<LinearUnit> toMulti,
 			UncertainDouble uncertainValue) {
@@ -686,7 +680,7 @@ public final class Presenter {
 				throw this.viewError("Could not convert between %s and %s",
 						fromUnit, toUnit);
 		}
-		
+
 		final LinearUnitValue initValue;
 		if (fromUnit instanceof LinearUnit) {
 			final var fromLinear = (LinearUnit) fromUnit;
@@ -695,46 +689,46 @@ public final class Presenter {
 			initValue = UnitValue.of(fromUnit, uncertainValue.value())
 					.convertToBase(NameSymbol.EMPTY);
 		}
-		
-		final List<LinearUnitValue> converted = initValue
+
+		final var converted = initValue
 				.convertToMultiple(toMulti);
-		final String toExpression = this.linearUnitValueSumToString(converted);
+		final var toExpression = this.linearUnitValueSumToString(converted);
 		return UnitConversionRecord.valueOf(fromUnitString, toExpression,
 				inputValueString, "");
-		
+
 	}
-	
+
 	private UnitConversionRecord convertUnitToUnit(String fromUnitString,
 			String toUnitString, String inputValueString, Unit fromUnit,
 			Unit toUnit, UncertainDouble uncertainValue) {
 		if (!fromUnit.canConvertTo(toUnit))
 			throw this.viewError("Could not convert between %s and %s", fromUnit,
 					toUnit);
-			
+
 		// convert - we will need to erase uncertainty for non-linear units, so
 		// we need to treat linear and non-linear units differently
 		final String outputValueString;
 		if (fromUnit instanceof LinearUnit && toUnit instanceof LinearUnit) {
-			final LinearUnit fromLinear = (LinearUnit) fromUnit;
-			final LinearUnit toLinear = (LinearUnit) toUnit;
-			final LinearUnitValue initialValue = LinearUnitValue.of(fromLinear,
+			final var fromLinear = (LinearUnit) fromUnit;
+			final var toLinear = (LinearUnit) toUnit;
+			final var initialValue = LinearUnitValue.of(fromLinear,
 					uncertainValue);
-			final LinearUnitValue converted = initialValue.convertTo(toLinear);
-			
+			final var converted = initialValue.convertTo(toLinear);
+
 			outputValueString = this.numberDisplayRule.apply(converted.getValue());
 		} else {
-			final UnitValue initialValue = UnitValue.of(fromUnit,
+			final var initialValue = UnitValue.of(fromUnit,
 					uncertainValue.value());
-			final UnitValue converted = initialValue.convertTo(toUnit);
-			
+			final var converted = initialValue.convertTo(toUnit);
+
 			outputValueString = this.numberDisplayRule
 					.apply(UncertainDouble.of(converted.getValue(), 0));
 		}
-		
+
 		return UnitConversionRecord.valueOf(fromUnitString, toUnitString,
 				inputValueString, outputValueString);
 	}
-	
+
 	/**
 	 * @return true iff duplicate units are shown in unit lists
 	 * @since 2022-03-30
@@ -742,26 +736,26 @@ public final class Presenter {
 	public boolean duplicatesShown() {
 		return this.showDuplicates;
 	}
-	
+
 	/**
 	 * @return text in About file
 	 * @since 2022-02-19
 	 */
-	public final String getAboutText() {
+	public String getAboutText() {
 		return Presenter.getLinesFromResource("/about.txt").stream()
 				.map(Presenter::withoutComments).collect(Collectors.joining("\n"))
 				.replaceAll("\\[VERSION\\]", ProgramInfo.VERSION.toString())
 				.replaceAll("\\[LOADSTATS\\]", wrapString(this.loadStatMsg(), 72));
 	}
-	
+
 	/**
 	 * @return set of all locales available to select
 	 * @since 2025-02-21
 	 */
-	public final Set<String> getAvailableLocales() {
+	public Set<String> getAvailableLocales() {
 		return this.locales.keySet();
 	}
-	
+
 	/**
 	 * Gets a name for this dimension using the database
 	 *
@@ -769,28 +763,28 @@ public final class Presenter {
 	 * @return name of dimension
 	 * @since 2022-04-16
 	 */
-	final String getDimensionName(ObjectProduct<BaseDimension> dimension) {
+	String getDimensionName(ObjectProduct<BaseDimension> dimension) {
 		// find this dimension in the database and get its name
 		// if it isn't there, use the dimension's toString instead
 		return this.database.dimensionMap().values().stream()
 				.filter(d -> d.equals(dimension)).findAny().map(Nameable::getName)
 				.orElse(dimension.toString(Nameable::getName));
 	}
-	
+
 	/**
-	 * Gets the correct text for a provided ID.
-	 * If this text is available in the user's locale, that text is provided.
-	 * Otherwise, text is taken from the system default locale {@link #DEFAULT_LOCALE}.
-	 * 
+	 * Gets the correct text for a provided ID. If this text is available in the
+	 * user's locale, that text is provided. Otherwise, text is taken from the
+	 * system default locale {@link #DEFAULT_LOCALE}.
+	 *
 	 * @param textID ID of text to get (used in locale files)
 	 * @return text to be displayed
 	 */
 	public String getLocalizedText(String textID) {
-		final Map<String, String> userLocale = this.locales.get(this.userLocale);
-		final Map<String, String> defaultLocale = this.locales.get(DEFAULT_LOCALE);
+		final var userLocale = this.locales.get(this.userLocale);
+		final var defaultLocale = this.locales.get(DEFAULT_LOCALE);
 		return userLocale.getOrDefault(textID, defaultLocale.get(textID));
 	}
-	
+
 	/**
 	 * @return the rule that is used by this presenter to convert numbers into
 	 *         strings
@@ -799,7 +793,7 @@ public final class Presenter {
 	public Function<UncertainDouble, String> getNumberDisplayRule() {
 		return this.numberDisplayRule;
 	}
-	
+
 	/**
 	 * @return the rule that is used by this presenter to convert strings into
 	 *         numbers
@@ -809,7 +803,7 @@ public final class Presenter {
 	private Function<String, UncertainDouble> getNumberParsingRule() {
 		return this.numberParsingRule;
 	}
-	
+
 	/**
 	 * @return the rule that determines whether a set of prefixes is valid
 	 * @since 2022-04-19
@@ -817,7 +811,7 @@ public final class Presenter {
 	public Predicate<List<UnitPrefix>> getPrefixRepetitionRule() {
 		return this.prefixRepetitionRule;
 	}
-	
+
 	/**
 	 * @return the rule that determines which units are prefixed
 	 * @since 2022-07-08
@@ -825,15 +819,7 @@ public final class Presenter {
 	public Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> getSearchRule() {
 		return this.searchRule;
 	}
-	
-	/**
-	 * @return user's selected locale
-	 * @since 2025-02-21
-	 */
-	public String getUserLocale() {
-		return userLocale;
-	}
-	
+
 	/**
 	 * @return a search rule that shows all single prefixes
 	 * @since 2022-07-08
@@ -842,7 +828,15 @@ public final class Presenter {
 		return PrefixSearchRule.getCoherentOnlyRule(
 				new HashSet<>(this.database.prefixMap(true).values()));
 	}
-	
+
+	/**
+	 * @return user's selected locale
+	 * @since 2025-02-21
+	 */
+	public String getUserLocale() {
+		return userLocale;
+	}
+
 	/**
 	 * @return the view associated with this presenter
 	 * @since 2022-04-19
@@ -850,7 +844,7 @@ public final class Presenter {
 	public View getView() {
 		return this.view;
 	}
-	
+
 	/**
 	 * Accepts a list of errors. If that list is non-empty, prints an error
 	 * message and alerts the user.
@@ -859,7 +853,7 @@ public final class Presenter {
 	 */
 	private void handleLoadErrors(List<LoadingException> errors) {
 		if (!errors.isEmpty()) {
-			final String errorMessage = String.format(
+			final var errorMessage = String.format(
 					"%d error(s) happened while loading file:\n%s\n", errors.size(),
 					errors.stream().map(Throwable::getMessage)
 							.collect(Collectors.joining("\n")));
@@ -868,13 +862,13 @@ public final class Presenter {
 					errorMessage);
 		}
 	}
-	
+
 	/**
 	 * @return whether or not the provided unit is semi-metric (i.e. an
 	 *         exception)
 	 * @since 2022-04-16
 	 */
-	final boolean isSemiMetric(Unit u) {
+	boolean isSemiMetric(Unit u) {
 		// determine if u is an exception
 		final var primaryName = u.getPrimaryName();
 		final var symbol = u.getSymbol();
@@ -884,7 +878,7 @@ public final class Presenter {
 						&& this.metricExceptions.contains(symbol.orElseThrow())
 				|| sharesAnyElements(this.metricExceptions, u.getOtherNames());
 	}
-	
+
 	/**
 	 * Convert a list of LinearUnitValues that you would get from a unit-set
 	 * conversion to a string. All but the last have their numbers rendered as
@@ -893,18 +887,17 @@ public final class Presenter {
 	 *
 	 * @since 2024-08-16
 	 */
-	private final String linearUnitValueSumToString(
-			List<LinearUnitValue> values) {
-		final String integerPart = values.subList(0, values.size() - 1).stream()
+	private String linearUnitValueSumToString(List<LinearUnitValue> values) {
+		final var integerPart = values.subList(0, values.size() - 1).stream()
 				.map(Presenter::linearUnitValueIntToString)
 				.collect(Collectors.joining(" + "));
-		final LinearUnitValue last = values.get(values.size() - 1);
+		final var last = values.get(values.size() - 1);
 		return integerPart + " + " + this.numberDisplayRule.apply(last.getValue())
 				+ " " + last.getUnit();
 	}
-	
+
 	private void loadExceptionFile(Path exceptionFile) {
-		try (Stream<String> lines = Files.lines(exceptionFile)) {
+		try (var lines = Files.lines(exceptionFile)) {
 			lines.map(Presenter::withoutComments)
 					.forEach(this.metricExceptions::add);
 		} catch (final IOException e) {
@@ -913,7 +906,54 @@ public final class Presenter {
 							+ exceptionFile + "\": " + e.getLocalizedMessage());
 		}
 	}
+
+	/**
+	 * Loads all available locales, including custom ones, into a map.
+	 * @return map containing locales
+	 */
+	private Map<String, Map<String, String>> loadLocales() {
+		final Map<String, Map<String, String>> locales = new HashMap<>();
+		for (final String localeName : LOCAL_LOCALES) {
+			final Map<String, String> locale = new HashMap<>();
+			String filename = "/locales/" + localeName + ".txt";
+			getLinesFromResource(filename).forEach(line -> addLocaleLine(locale, line));
+			locales.put(localeName, locale);	
+		}
+		
+		if (Files.exists(USER_LOCALES_DIR)) {
+			try {
+				Files.list(USER_LOCALES_DIR).forEach(
+						localeFile -> {
+							try {
+								addLocaleFile(locales, localeFile);
+							} catch (IOException e) {
+								e.printStackTrace();
+							}
+						});
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+		}
+		return locales;
+	}
 	
+	private void addLocaleFile(Map<String, Map<String, String>> locales, Path file) throws IOException {
+		final Map<String, String> locale = new HashMap<>();
+		String fileName = file.getName(file.getNameCount()-1).toString();
+		String localeName = fileName.substring(0, fileName.length()-4);
+		Files.lines(file).forEach(line -> addLocaleLine(locale, line));
+		locales.put(localeName, locale);
+	}
+	
+	private void addLocaleLine(Map<String, String> locale, String line) {
+		String[] parts = line.split("=", 2);
+		if (parts.length < 2) {
+			return;
+		}
+			
+		locale.put(parts[0], parts[1]);
+	}
+
 	/**
 	 * Loads settings from the user's settings file and applies them to the
 	 * presenter.
@@ -924,8 +964,8 @@ public final class Presenter {
 	void loadSettings(Path settingsFile) {
 		for (final Map.Entry<String, String> setting : this
 				.settingsFromFile(settingsFile)) {
-			final String value = setting.getValue();
-			
+			final var value = setting.getValue();
+
 			switch (setting.getKey()) {
 			// set manually to avoid the unnecessary saving of the non-manual
 			// methods
@@ -949,26 +989,29 @@ public final class Presenter {
 				this.database.setPrefixRepetitionRule(this.prefixRepetitionRule);
 				break;
 			case "one_way":
-				this.oneWayConversionEnabled = Boolean.valueOf(value);
+				this.oneWayConversionEnabled = Boolean.parseBoolean(value);
 				break;
 			case "include_duplicates":
-				this.showDuplicates = Boolean.valueOf(value);
+				this.showDuplicates = Boolean.parseBoolean(value);
 				break;
 			case "search_prefix_rule":
 				this.setSearchRuleFromString(value);
 				break;
+			case "locale":
+				this.setUserLocale(value);
+				break;
 			default:
 				System.err.printf("Warning: unrecognized setting \"%s\".%n",
 						setting.getKey());
 				break;
 			}
 		}
-		
+
 		if (this.view.getPresenter() != null) {
 			this.updateView();
 		}
 	}
-	
+
 	/**
 	 * @return a message showing how much stuff has been loaded
 	 * @since 2024-08-22
@@ -985,37 +1028,37 @@ public final class Presenter {
 				this.database.unitSetMap().size(),
 				this.database.dimensionMap().size());
 	}
-	
+
 	/**
 	 * @return true iff the One-Way Conversion feature is available (views that
 	 *         show units as a list will have metric units removed from the From
 	 *         unit list and imperial/USC units removed from the To unit list)
-	 * 
+	 *
 	 * @since 2022-03-30
 	 */
 	public boolean oneWayConversionEnabled() {
 		return this.oneWayConversionEnabled;
 	}
-	
+
 	/**
 	 * Completes creation of the presenter. This part of the initialization
 	 * depends on the view's functions, so it cannot be run if the components
 	 * they depend on are not created yet.
-	 * 
+	 *
 	 * @since 2022-02-26
 	 */
 	public void postViewInitialize() {
 		// unit conversion specific stuff
 		if (this.view instanceof UnitConversionView) {
-			final UnitConversionView ucview = (UnitConversionView) this.view;
+			final var ucview = (UnitConversionView) this.view;
 			ucview.setDimensionNames(this.database.dimensionMap().keySet());
 		}
-		
+
 		this.updateView();
 	}
-	
+
 	void prefixSelected() {
-		final Optional<String> selectedPrefixName = this.view
+		final var selectedPrefixName = this.view
 				.getViewedPrefixName();
 		final Optional<UnitPrefix> selectedPrefix = selectedPrefixName
 				.map(name -> this.database.containsPrefixName(name)
@@ -1025,16 +1068,16 @@ public final class Presenter {
 				.ifPresent(prefix -> this.view.showPrefix(prefix.getNameSymbol(),
 						String.valueOf(prefix.getMultiplier())));
 	}
-	
+
 	/**
 	 * Saves the presenter's current settings to the config file, creating it if
 	 * it doesn't exist.
-	 * 
+	 *
 	 * @return false iff the presenter could not write to the file
 	 * @since 2022-04-19
 	 */
 	public boolean saveSettings() {
-		final Path configDir = CONFIG_FILE.getParent();
+		final var configDir = CONFIG_FILE.getParent();
 		if (!Files.exists(configDir)) {
 			try {
 				Files.createDirectories(configDir);
@@ -1042,19 +1085,19 @@ public final class Presenter {
 				return false;
 			}
 		}
-		
+
 		return this.writeSettings(CONFIG_FILE);
 	}
-	
+
 	private void setDisplayRuleFromString(String ruleString) {
-		final String[] tokens = ruleString.split(" ");
+		final var tokens = ruleString.split(" ");
 		switch (tokens[0]) {
 		case "FIXED_DECIMALS":
-			final int decimals = Integer.parseInt(tokens[1]);
+			final var decimals = Integer.parseInt(tokens[1]);
 			this.numberDisplayRule = StandardDisplayRules.fixedDecimals(decimals);
 			break;
 		case "FIXED_PRECISION":
-			final int sigDigs = Integer.parseInt(tokens[1]);
+			final var sigDigs = Integer.parseInt(tokens[1]);
 			this.numberDisplayRule = StandardDisplayRules.fixedPrecision(sigDigs);
 			break;
 		case "UNCERTAINTY_BASED":
@@ -1066,7 +1109,7 @@ public final class Presenter {
 			break;
 		}
 	}
-	
+
 	/**
 	 * @param numberDisplayRule the new rule that will be used by this presenter
 	 *                          to convert numbers into strings
@@ -1076,7 +1119,7 @@ public final class Presenter {
 			Function<UncertainDouble, String> numberDisplayRule) {
 		this.numberDisplayRule = numberDisplayRule;
 	}
-	
+
 	/**
 	 * @param numberParsingRule the new rule that will be used by this presenter
 	 *                          to convert strings into numbers
@@ -1087,7 +1130,7 @@ public final class Presenter {
 			Function<String, UncertainDouble> numberParsingRule) {
 		this.numberParsingRule = numberParsingRule;
 	}
-	
+
 	/**
 	 * @param oneWayConversionEnabled whether not one-way conversion should be
 	 *                                enabled
@@ -1098,7 +1141,7 @@ public final class Presenter {
 		this.oneWayConversionEnabled = oneWayConversionEnabled;
 		this.updateView();
 	}
-	
+
 	/**
 	 * @param prefixRepetitionRule the rule that determines whether a set of
 	 *                             prefixes is valid
@@ -1109,7 +1152,7 @@ public final class Presenter {
 		this.prefixRepetitionRule = prefixRepetitionRule;
 		this.database.setPrefixRepetitionRule(prefixRepetitionRule);
 	}
-	
+
 	/**
 	 * @param searchRule A rule that accepts a prefixless name-unit pair and
 	 *                   returns a map mapping names to prefixed versions of that
@@ -1121,7 +1164,7 @@ public final class Presenter {
 			Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> searchRule) {
 		this.searchRule = searchRule;
 	}
-	
+
 	private void setSearchRuleFromString(String ruleString) {
 		switch (ruleString) {
 		case "NO_PREFIXES":
@@ -1139,7 +1182,7 @@ public final class Presenter {
 					ruleString);
 		}
 	}
-	
+
 	/**
 	 * @param showDuplicateUnits whether or not duplicate units should be shown
 	 * @since 2022-03-30
@@ -1148,18 +1191,9 @@ public final class Presenter {
 		this.showDuplicates = showDuplicateUnits;
 		this.updateView();
 	}
-	
-	/**
-	 * Sets the user's locale, updating the view.
-	 * @param userLocale locale to use
-	 */
-	public void setUserLocale(String userLocale) {
-		this.userLocale = userLocale;
-		this.view.updateText();
-	}
-	
+
 	private List<Map.Entry<String, String>> settingsFromFile(Path settingsFile) {
-		try (Stream<String> lines = Files.lines(settingsFile)) {
+		try (var lines = Files.lines(settingsFile)) {
 			return lines.map(Presenter::withoutComments)
 					.filter(line -> !line.isBlank()).map(Presenter::parseSettingLine)
 					.toList();
@@ -1169,7 +1203,17 @@ public final class Presenter {
 			return null;
 		}
 	}
-	
+
+	/**
+	 * Sets the user's locale, updating the view.
+	 *
+	 * @param userLocale locale to use
+	 */
+	public void setUserLocale(String userLocale) {
+		this.userLocale = userLocale;
+		this.view.updateText();
+	}
+
 	/**
 	 * Shows a unit in the unit viewer
 	 *
@@ -1178,53 +1222,53 @@ public final class Presenter {
 	 */
 	private void showUnit(Unit u) {
 		final var nameSymbol = u.getNameSymbol();
-		final boolean isBase = u instanceof BaseUnit
+		final var isBase = u instanceof BaseUnit
 				|| u instanceof LinearUnit && ((LinearUnit) u).isBase();
 		final var definition = isBase ? "(Base unit)" : u.toDefinitionString();
 		final var dimensionString = this.getDimensionName(u.getDimension());
 		final var unitType = UnitType.getType(u, this::isSemiMetric);
 		this.view.showUnit(nameSymbol, definition, dimensionString, unitType);
 	}
-	
+
 	/**
 	 * Runs whenever a unit name is selected in the unit viewer. Gets the
 	 * description of a unit and displays it.
-	 * 
+	 *
 	 * @since 2022-04-10
 	 */
 	void unitNameSelected() {
 		// get selected unit, if it's there and valid
-		final Optional<String> selectedUnitName = this.view.getViewedUnitName();
+		final var selectedUnitName = this.view.getViewedUnitName();
 		final Optional<Unit> selectedUnit = selectedUnitName
 				.map(unitName -> this.database.containsUnitName(unitName)
 						? this.database.getUnit(unitName)
 						: null);
 		selectedUnit.ifPresent(this::showUnit);
 	}
-	
+
 	/**
 	 * Updates the view's From and To units, if it has some
-	 * 
+	 *
 	 * @since 2021-12-15
 	 */
 	public void updateView() {
 		if (this.view instanceof UnitConversionView) {
-			final UnitConversionView ucview = (UnitConversionView) this.view;
+			final var ucview = (UnitConversionView) this.view;
 			final var selectedDimensionName = ucview.getSelectedDimensionName();
-			
+
 			// load units & prefixes into viewers
 			this.view.setViewableUnitNames(
 					this.database.unitMapPrefixless(this.showDuplicates).keySet());
 			this.view.setViewablePrefixNames(
 					this.database.prefixMap(this.showDuplicates).keySet());
-			
+
 			// get From and To units
 			var fromUnits = this.database.unitMapPrefixless(this.showDuplicates)
 					.entrySet().stream();
 			var toUnits = this.database.unitMapPrefixless(this.showDuplicates)
 					.entrySet().stream();
 			var unitSets = this.database.unitSetMap().entrySet().stream();
-			
+
 			// filter by dimension, if one is selected
 			if (selectedDimensionName.isPresent()) {
 				final var viewDimension = this.database
@@ -1236,7 +1280,7 @@ public final class Presenter {
 				unitSets = unitSets.filter(us -> viewDimension
 						.equals(us.getValue().get(0).getDimension()));
 			}
-			
+
 			// filter by unit type, if desired
 			if (this.oneWayConversionEnabled) {
 				fromUnits = fromUnits.filter(u -> UnitType.getType(u.getValue(),
@@ -1247,7 +1291,7 @@ public final class Presenter {
 				unitSets = unitSets
 						.filter(us -> this.metricExceptions.contains(us.getKey()));
 			}
-			
+
 			// set unit names
 			ucview.setFromUnitNames(fromUnits.flatMap(this::applySearchRule)
 					.map(Map.Entry::getKey).collect(Collectors.toSet()));
@@ -1259,7 +1303,7 @@ public final class Presenter {
 			ucview.setToUnitNames(toNames);
 		}
 	}
-	
+
 	/**
 	 * @param message message to add
 	 * @param args    string formatting arguments for message
@@ -1271,15 +1315,15 @@ public final class Presenter {
 		return new AssertionError("View Programming Error (from " + this.view
 				+ "): " + String.format(message, args));
 	}
-	
+
 	/**
 	 * Saves the presenter's settings to the user settings file.
-	 * 
+	 *
 	 * @param settingsFile file settings should be saved to
 	 * @since 2021-12-15
 	 */
 	boolean writeSettings(Path settingsFile) {
-		try (BufferedWriter writer = Files.newBufferedWriter(settingsFile)) {
+		try (var writer = Files.newBufferedWriter(settingsFile)) {
 			writer.write(String.format("number_display_rule=%s\n",
 					displayRuleToString(this.numberDisplayRule)));
 			writer.write(
@@ -1290,6 +1334,7 @@ public final class Presenter {
 					String.format("include_duplicates=%s\n", this.showDuplicates));
 			writer.write(String.format("search_prefix_rule=%s\n",
 					searchRuleToString(this.searchRule)));
+			writer.write(String.format("locale=%s\n", this.userLocale));
 			return true;
 		} catch (final IOException e) {
 			e.printStackTrace();
diff --git a/src/main/java/sevenUnitsGUI/TabbedView.java b/src/main/java/sevenUnitsGUI/TabbedView.java
index 493fc10..cb0a4d2 100644
--- a/src/main/java/sevenUnitsGUI/TabbedView.java
+++ b/src/main/java/sevenUnitsGUI/TabbedView.java
@@ -218,7 +218,8 @@ final class TabbedView implements ExpressionConversionView, UnitConversionView {
 		
 		// initialize important components
 		this.presenter = new Presenter(this);
-		this.frame = new JFrame("7Units " + ProgramInfo.VERSION);
+		this.frame = new JFrame(this.presenter.getLocalizedText("tv.title")
+				.replace("[v]", ProgramInfo.VERSION.toString()));
 		this.frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
 		
 		// master components (those that contain everything else within them)
diff --git a/src/main/resources/locales/en.txt b/src/main/resources/locales/en.txt
new file mode 100644
index 0000000..9d453c9
--- /dev/null
+++ b/src/main/resources/locales/en.txt
@@ -0,0 +1 @@
+tv.title=7Units [v]
\ No newline at end of file
diff --git a/src/main/resources/locales/fr.txt b/src/main/resources/locales/fr.txt
new file mode 100644
index 0000000..1d08fda
--- /dev/null
+++ b/src/main/resources/locales/fr.txt
@@ -0,0 +1 @@
+tv.title=7Unités [v]
\ No newline at end of file