feat: enhance localization handling by adding xcstringsParsingKey method and updating parsing logic

Sources/CrowdinSDK/Providers/Crowdin/LocalizationDownloader/CrowdinLocalizationDownloader.swift

@@ -80,7 +80,8 @@ class CrowdinLocalizationDownloader: CrowdinDownloaderProtocol {
             if let files = files {
                 let xcstringsFiles = files.filter({ $0.isXcstrings })
                 // For xcstrings we need to parse existing files when localization is changed, otherwise we wont get localization strings from xcstrings files.
-                self.parseXCStrings(files: xcstringsFiles, for: localization, context: context)
+                let xcstringsParsingKey = self.manifestManager.xcstringsParsingKey(for: localization)
+                self.parseXCStrings(files: xcstringsFiles, for: xcstringsParsingKey, context: context)
                 let notXcstringsFiles = files.filter({ !$0.isXcstrings })
                 let notXcstringsFilesToDownload = notXcstringsFiles.filter { self.manifestManager.hasFileChanged(filePath: $0, localization: localization) }
                 let xcStringsFilesToDownlaod = xcstringsFiles.filter({ self.manifestManager.hasFileChanged(filePath: $0, localization: self.manifestManager.xcstringsLanguage) })
@@ -165,7 +166,7 @@ class CrowdinLocalizationDownloader: CrowdinDownloaderProtocol {
 
         xcstrings.forEach { filePath in
             let download = CrowdinXcstringsDownloadOperation(filePath: filePath,
-                                                             localization: localization,
+                                                             localization: manifestManager.xcstringsParsingKey(for: localization),
                                                              xcstringsLanguage: manifestManager.xcstringsLanguage,
                                                              timestamp: timestamp,
                                                              contentDeliveryAPI: contentDeliveryAPI)

Sources/CrowdinSDK/Providers/Crowdin/ManifestManager/ManifestManager+LanguageResolver.swift

@@ -56,4 +56,28 @@ extension ManifestManager: LanguageResolver {
 
         return languages.first(where: { $0.id == crowdinLocalization })?.iOSLanguageCode
     }
+
+    /// Returns the language key used inside an xcstrings file for the given iOS localization.
+    ///
+    /// Standard Crowdin languages use their `osxLocale` as the xcstrings key (e.g. "de", "zh-Hans").
+    /// Custom languages have an `osxLocale` that acts as the iOS locale folder name (e.g. "tra", "SRXK")
+    /// but the xcstrings file stores their translations under the BCP 47 locale derived from the
+    /// custom language's `locale` field (e.g. "to" for "to-To", "sr-XK" for "sr-XK").
+    func xcstringsParsingKey(for localization: String) -> String {
+        let custom = customLanguages
+        guard let language = crowdinSupportedLanguage(for: localization),
+              custom.contains(where: { $0.id == language.id }) else {
+            // Standard language: the iOS localization is already the xcstrings key.
+            return localization
+        }
+        // Custom language: derive the xcstrings key from the locale field.
+        // Replace underscores with hyphens to get BCP 47 format, then strip a redundant
+        // region subtag when it matches the language subtag (e.g. "to-To" → "to").
+        let normalizedLocale = language.locale.replacingOccurrences(of: "_", with: "-")
+        let parts = normalizedLocale.components(separatedBy: "-")
+        if parts.count == 2 && parts[0].lowercased() == parts[1].lowercased() {
+            return parts[0]
+        }
+        return normalizedLocale
+    }
 }