Use native iOS localization selection

apps/ios/GuideDogs.xcodeproj/project.pbxproj

@@ -532,6 +532,7 @@
 		914BAAFD2AD7483300CB2171 /* AudioEngineTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 914BAAFC2AD7483300CB2171 /* AudioEngineTest.swift */; };
 		914BAB012AD7490100CB2171 /* NavigationControllerTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 914BAB002AD7490100CB2171 /* NavigationControllerTest.swift */; };
 		D4A72B0131A1000100C0FFEE /* URLResourceIdentifierTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4A72B0031A1000100C0FFEE /* URLResourceIdentifierTest.swift */; };
+		D4A72B1131A2000100C0FFEE /* LocalizationContextTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4A72B1031A2000100C0FFEE /* LocalizationContextTest.swift */; };
 		915FF9F62ADE4BAF002B3690 /* AuthoredActivityContentTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 915FF9F42ADE3F91002B3690 /* AuthoredActivityContentTest.swift */; };
 		91C82AAD2A5DCF040086D126 /*  GeolocationManagerTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 91C82AAC2A5DCF040086D126 /*  GeolocationManagerTest.swift */; };
 		91C82ABE2A6B08500086D126 /* RouteGuidanceTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 91C82ABD2A6B08500086D126 /* RouteGuidanceTest.swift */; };
@@ -1324,6 +1325,7 @@
 		914BAAFC2AD7483300CB2171 /* AudioEngineTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AudioEngineTest.swift; sourceTree = "<group>"; };
 		914BAB002AD7490100CB2171 /* NavigationControllerTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NavigationControllerTest.swift; sourceTree = "<group>"; };
 		D4A72B0031A1000100C0FFEE /* URLResourceIdentifierTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = URLResourceIdentifierTest.swift; sourceTree = "<group>"; };
+		D4A72B1031A2000100C0FFEE /* LocalizationContextTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LocalizationContextTest.swift; sourceTree = "<group>"; };
 		914DEBCD2A3CE6B9007B161C /* UnitTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = UnitTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		914DEBDC2A3CE901007B161C /* GeometryUtilsTest.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GeometryUtilsTest.swift; sourceTree = "<group>"; };
 		915FF9F42ADE3F91002B3690 /* AuthoredActivityContentTest.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AuthoredActivityContentTest.swift; sourceTree = "<group>"; };
@@ -3510,12 +3512,21 @@
 				914BAAFB2AD747C200CB2171 /* Audio */,
 				91C82ABB2A6B03790086D126 /* Behaviors */,
 				91C82AB52A67182E0086D126 /* Data */,
+				D4A72B1231A2000100C0FFEE /* Language */,
 				91C82AA62A4F56A70086D126 /* Sensors */,
 				914DEBD92A3CE7E6007B161C /* App */,
 			);
 			path = UnitTests;
 			sourceTree = "<group>";
 		};
+		D4A72B1231A2000100C0FFEE /* Language */ = {
+			isa = PBXGroup;
+			children = (
+				D4A72B1031A2000100C0FFEE /* LocalizationContextTest.swift */,
+			);
+			path = Language;
+			sourceTree = "<group>";
+		};
 		914DEBD92A3CE7E6007B161C /* App */ = {
 			isa = PBXGroup;
 			children = (
@@ -4732,6 +4743,7 @@
 				666CA3EAAA904E6EBFA10A53 /* NaviLensWakeOnForegroundTest.swift in Sources */,
 				914BAB012AD7490100CB2171 /* NavigationControllerTest.swift in Sources */,
 				D4A72B0131A1000100C0FFEE /* URLResourceIdentifierTest.swift in Sources */,
+				D4A72B1131A2000100C0FFEE /* LocalizationContextTest.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

apps/ios/GuideDogs/Code/Language/Localization/LocalizationContext.swift

@@ -3,6 +3,7 @@
 //  Soundscape
 //
 //  Copyright (c) Microsoft Corporation.
+//  Copyright (c) Soundscape Community Contributors.
 //  Licensed under the MIT License.
 //
 
@@ -79,36 +80,24 @@ class LocalizationContext {
     }
 
     /// The current app locale. This will return one of the following:
-    /// 1. The user selected app locale (if a selection has been made)
-    /// 2. The device locale (if supported by the app)
-    /// 3. The default English locale
+    /// 1. The user-selected app locale (if a valid selection has been made)
+    /// 2. The localization selected by iOS from the user's preferred languages
+    /// 3. The app's development locale
     static var currentAppLocale: Locale {
         get {
-            let currentAppLocale: Locale
-
-            // Check if the user has selected a locale
-            if let locale = SettingsContext.shared.locale {
-                currentAppLocale = locale
-            } else if let firstSupportedLocale = firstSupportedLocale {
-                // If not, check if the device's locale is supported
-                currentAppLocale = firstSupportedLocale
-            } else {
-                // If not, fallback to the default English locale (en-US or en-GB)
-                currentAppLocale = deviceLocale.defaultEnglish
-            }
-
-            // Store the locale and bundle
-            if currentAppLocale != _currentAppLocale {
-                _currentAppLocale = currentAppLocale
-                currentAppLocaleBundle = Bundle(locale: currentAppLocale)
-            }
-
-            return currentAppLocale
+            return currentLocalization().locale
         }
         set(newLocale) {
+            guard let bundle = Bundle(locale: newLocale) else {
+                DDLogError("Localization error: Unsupported app locale \"\(newLocale.identifier)\"")
+                return
+            }
+
+            localizationLock.lock()
+            cachedLocalization = AppLocalization(locale: newLocale, bundle: bundle)
+            localizationLock.unlock()
+
             SettingsContext.shared.locale = newLocale
-            _currentAppLocale = newLocale
-            currentAppLocaleBundle = Bundle(locale: newLocale)!
 
             configureAccessibilityLanguage()
 
@@ -119,11 +108,14 @@ class LocalizationContext {
             }
         }
     }
-
-    static private var _currentAppLocale: Locale?
-    static private var currentAppLocaleBundle: Bundle?
-
-    static private let defaultEnglishBundle = Bundle(locale: deviceLocale.defaultEnglish)!
+
+    private struct AppLocalization {
+        let locale: Locale
+        let bundle: Bundle
+    }
+
+    private static let localizationLock = NSLock()
+    private static var cachedLocalization: AppLocalization?
 
     static var currentLanguageCode: String {
         return currentAppLocale.languageCode ?? defaultLanguageCode
@@ -134,44 +126,64 @@ class LocalizationContext {
     }
 
     /// The development app locale ("en-US")
-    static var developmentLocale = Bundle.main.developmentLocale!
-    
+    static let developmentLocale = Bundle.main.developmentLocale ?? Locale.enUS
+
     static private let defaultDevelopmentBundle = Bundle(locale: developmentLocale)!
-
-    private static var _firstSupportedLocale: Locale?
-
-    static var firstSupportedLocale: Locale? {
-        if let firstSupportedLocale = _firstSupportedLocale {
-            return firstSupportedLocale
+
+    private static func currentLocalization() -> AppLocalization {
+        let developmentBundle = defaultDevelopmentBundle
+
+        localizationLock.lock()
+        defer { localizationLock.unlock() }
+
+        if let cachedLocalization {
+            return cachedLocalization
         }
-
-        for preferredLocale in Locale.preferredLocales {
-            if preferredLocale == Locale.enUS {
-                _firstSupportedLocale = Locale.enUS
-                break
-            } else if preferredLocale == Locale.enGB {
-                _firstSupportedLocale = Locale.enGB
-                break
-            } else if preferredLocale.languageCode == Locale.en.languageCode {
-                _firstSupportedLocale = deviceLocale.defaultEnglish
-                break
-            } else if let locale = supportedLocales.first(where: { $0 == preferredLocale }) {
-                _firstSupportedLocale = locale
-                break
-            }
+
+        let locale = resolveAppLocale(
+            selectedLocale: SettingsContext.shared.locale,
+            supportedLocales: supportedLocales,
+            preferredLocalization: Bundle.main.preferredLocalizations.first,
+            developmentLocalization: Bundle.main.developmentLocalization
+        )
+        let localization = AppLocalization(
+            locale: locale,
+            bundle: Bundle(locale: locale) ?? developmentBundle
+        )
+        cachedLocalization = localization
+
+        return localization
+    }
+
+    static func resolveAppLocale(
+        selectedLocale: Locale?,
+        supportedLocales: [Locale],
+        preferredLocalization: String?,
+        developmentLocalization: String?
+    ) -> Locale {
+        if let selectedLocale,
+           let supportedLocale = supportedLocale(matching: selectedLocale.identifier, in: supportedLocales) {
+            return supportedLocale
         }
-        // Fallback: match only on language part if no exact match found
-        if _firstSupportedLocale == nil {
-            for preferredLocale in Locale.preferredLocales {
-                if let languageCode = preferredLocale.languageCode,
-                   let locale = supportedLocales.first(where: { $0.languageCode == languageCode }) {
-                    _firstSupportedLocale = locale
-                    break
-                }
-            }
+
+        if let preferredLocalization,
+           let supportedLocale = supportedLocale(matching: preferredLocalization, in: supportedLocales) {
+            return supportedLocale
+        }
+
+        if let developmentLocalization {
+            return supportedLocale(matching: developmentLocalization, in: supportedLocales)
+                ?? Locale(identifier: developmentLocalization)
+        }
+
+        return Locale.enUS
+    }
+
+    private static func supportedLocale(matching identifier: String, in supportedLocales: [Locale]) -> Locale? {
+        let normalizedIdentifier = Locale(identifier: identifier).identifierHyphened.lowercased()
+        return supportedLocales.first {
+            $0.identifierHyphened.lowercased() == normalizedIdentifier
         }
-
-        return _firstSupportedLocale
     }
 
     // MARK: Properties
@@ -217,36 +229,36 @@ class LocalizationContext {
             DDLogWarn("Localized string error: key is nil")
             return key
         }
-
-        // If the current language does not contain the translation for the key, use the fallback language
-        return NSLocalizedString(key,
-                                 bundle: currentAppLocaleBundle ?? defaultEnglishBundle,
-                                 value: localizedStringFallbackLanguage(key),
-                                 comment: "")
+
+        let localization = currentLocalization()
+
+        return localizedString(
+            key,
+            bundle: localization.bundle,
+            fallbackBundle: defaultDevelopmentBundle
+        )
     }
-    
-    private static func localizedStringFallbackLanguage(_ key: String) -> String {
+
+    static func localizedString(_ key: String, bundle: Bundle, fallbackBundle: Bundle) -> String {
         guard !key.isEmpty else {
             DDLogWarn("Localized string error: key is nil")
             return key
         }
-
-        let defaultEnglishLocale = deviceLocale.defaultEnglish
-
-        // Try the default English language ("en-US" or "en-GB")
-        if let string = nsLocalizedString(key, bundle: defaultEnglishBundle) {
-            return string
-        }
-
-        // If the default English language was "en-GB", try "en-US" (the base development language)
-        if defaultEnglishLocale != developmentLocale,
-            let string = nsLocalizedString(key, bundle: defaultDevelopmentBundle) {
-            return string
+
+        let fallback: String
+        if let developmentString = nsLocalizedString(key, bundle: fallbackBundle) {
+            fallback = developmentString
+        } else {
+            DDLogWarn("Localization error: Localized string not found for key \"\(key)\"")
+            fallback = key
         }
-
-        DDLogWarn("Localization error: Localized string not found for key \"\(key)\"")
 
-        return key
+        return NSLocalizedString(
+            key,
+            bundle: bundle,
+            value: fallback,
+            comment: ""
+        )
     }
 
     /// Returns the localized string using the native `NSLocalizedString` function,
@@ -321,29 +333,12 @@ extension Bundle {
 }
 
 extension Locale {
-    /// The locale for English (without region)
-    static let en = Locale(identifier: "en")
-
     /// The locale for English (United States)
     static let enUS = Locale(identifier: "en-US")
 
-    /// The locale for English (United Kingdom)
-    static let enGB = Locale(identifier: "en-GB")
-
     /// Locale for French (France)
     static let frFr = Locale(identifier: "fr-FR")
 
-    /// Returns the `preferredLanguages` objects as `Locale` objects
-    static var preferredLocales: [Locale] {
-        return Locale.preferredLanguages.map { Locale(identifier: $0) }
-    }
-
-    /// The default English locale. This follows the suggested standard were users in the US will default to
-    /// "English (United States)", and users outside the US will default to "English (United Kingdom)".
-    var defaultEnglish: Locale {
-        return self.identifier == Locale.enUS.identifier ? Locale.enUS : Locale.enGB
-    }
-
     /// Returns the identifier with a hyphen ("-"), if an underscore ("_") is used, e.g. "en_US" -> "en-US".
     ///
     /// Information about locale identifiers: