🌐 Preserve locale subtags in language redirects

assets/js/language-redirect.js

@@ -24,19 +24,62 @@
       return "";
     }
 
-    return value.trim().toLowerCase();
+    return value.trim().toLowerCase().replace(/_/g, "-");
   }
 
-  function normalizeLanguage(value) {
-    return normalizeLanguageTag(value).split("-")[0];
-  }
+  function getBaseLanguage(value) {
+    var languageTag = normalizeLanguageTag(value);
 
-  function getTranslationLanguage(translation) {
-    if (!translation) {
+    if (!languageTag) {
       return "";
     }
 
-    return normalizeLanguageTag(translation.lang || translation.languageCode);
+    return languageTag.split("-")[0];
+  }
+
+  function getTranslationTags(translation) {
+    if (!translation) {
+      return [];
+    }
+
+    var tags = [];
+    var values = [translation.lang, translation.languageCode];
+
+    for (var i = 0; i < values.length; i += 1) {
+      var languageTag = normalizeLanguageTag(values[i]);
+
+      if (languageTag && tags.indexOf(languageTag) === -1) {
+        tags.push(languageTag);
+      }
+    }
+
+    return tags;
+  }
+
+  function getCanonicalTranslationTag(translation) {
+    var tags = getTranslationTags(translation);
+
+    if (!tags.length) {
+      return "";
+    }
+
+    return tags.reduce(function (bestTag, languageTag) {
+      if (languageTag.split("-").length > bestTag.split("-").length) {
+        return languageTag;
+      }
+
+      return bestTag;
+    }, tags[0]);
+  }
+
+  function translationHasTag(translation, languageTag) {
+    var normalizedTag = normalizeLanguageTag(languageTag);
+
+    if (!normalizedTag) {
+      return false;
+    }
+
+    return getTranslationTags(translation).indexOf(normalizedTag) !== -1;
   }
 
   function getAvailableTranslations() {
@@ -45,45 +88,74 @@
     }
 
     return config.translations.filter(function (translation) {
-      return translation && translation.url && normalizeLanguage(translation.lang || translation.languageCode);
+      return translation && translation.url && getTranslationTags(translation).length > 0;
     });
   }
 
   var translations = getAvailableTranslations();
 
-  function findTranslation(language) {
-    var languageTag = normalizeLanguageTag(language);
-    var baseLanguage = normalizeLanguage(language);
+  function findExactTranslation(languageTag) {
+    var normalizedTag = normalizeLanguageTag(languageTag);
+
+    if (!normalizedTag) {
+      return null;
+    }
+
+    for (var i = 0; i < translations.length; i += 1) {
+      if (translationHasTag(translations[i], normalizedTag)) {
+        return translations[i];
+      }
+    }
+
+    return null;
+  }
+
+  function findBaseTranslation(languageTag) {
+    var baseLanguage = getBaseLanguage(languageTag);
 
     if (!baseLanguage) {
       return null;
     }
 
     for (var i = 0; i < translations.length; i += 1) {
-      var translation = translations[i];
+      var tags = getTranslationTags(translations[i]);
 
-      if (
-        normalizeLanguageTag(translation.lang) === languageTag ||
-        normalizeLanguageTag(translation.languageCode) === languageTag
-      ) {
-        return translation;
-      }
-    }
-
-    for (var j = 0; j < translations.length; j += 1) {
-      var baseTranslation = translations[j];
-
-      if (
-        normalizeLanguage(baseTranslation.lang) === baseLanguage ||
-        normalizeLanguage(baseTranslation.languageCode) === baseLanguage
-      ) {
-        return baseTranslation;
+      for (var j = 0; j < tags.length; j += 1) {
+        if (getBaseLanguage(tags[j]) === baseLanguage) {
+          return translations[i];
+        }
       }
     }
 
     return null;
   }
 
+  function findBestTranslation(languageTag) {
+    var normalizedTag = normalizeLanguageTag(languageTag);
+
+    if (!normalizedTag) {
+      return null;
+    }
+
+    while (normalizedTag) {
+      var translation = findExactTranslation(normalizedTag);
+
+      if (translation) {
+        return translation;
+      }
+
+      var lastSubtagIndex = normalizedTag.lastIndexOf("-");
+
+      if (lastSubtagIndex === -1) {
+        break;
+      }
+
+      normalizedTag = normalizedTag.slice(0, lastSubtagIndex);
+    }
+
+    return findBaseTranslation(languageTag);
+  }
+
   function getStoredLanguage() {
     if (!storage || config.storedLanguageRedirect !== true) {
       return null;
@@ -114,7 +186,7 @@
     }
   }
 
-  function getBrowserLanguage() {
+  function getBrowserTranslation() {
     var languages = [];
 
     if (Array.isArray(navigator.languages)) {
@@ -126,15 +198,15 @@
     }
 
     for (var i = 0; i < languages.length; i += 1) {
-      var baseLanguage = normalizeLanguage(languages[i]);
+      var translation = findBestTranslation(languages[i]);
 
-      if (findTranslation(baseLanguage)) {
-        return baseLanguage;
+      if (translation) {
+        return translation;
       }
     }
 
-    if (config.fallbackLanguage && findTranslation(config.fallbackLanguage)) {
-      return config.fallbackLanguage;
+    if (config.fallbackLanguage) {
+      return findBestTranslation(config.fallbackLanguage);
     }
 
     return null;
@@ -156,15 +228,16 @@
     }
   }
 
-  function redirectToLanguage(language) {
-    var translation = findTranslation(language);
-
+  function redirectToTranslation(translation) {
     if (!translation || !translation.url) {
       return false;
     }
 
-    var currentLanguage = normalizeLanguageTag(config.currentLanguage || config.currentLanguageCode);
-    var targetLanguage = getTranslationLanguage(translation);
+    var currentLanguage = getCanonicalTranslationTag({
+      lang: config.currentLanguage,
+      languageCode: config.currentLanguageCode
+    });
+    var targetLanguage = getCanonicalTranslationTag(translation);
 
     if (currentLanguage && targetLanguage && currentLanguage === targetLanguage) {
       return false;
@@ -180,6 +253,10 @@
     return true;
   }
 
+  function redirectToLanguage(language) {
+    return redirectToTranslation(findBestTranslation(language));
+  }
+
   function findTranslationByUrl(url) {
     var linkUrl = getUrl(url);
 
@@ -213,7 +290,7 @@
       var translation = findTranslationByUrl(link.href);
 
       if (translation) {
-        setStoredLanguage(getTranslationLanguage(translation));
+        setStoredLanguage(getCanonicalTranslationTag(translation));
       }
     });
   }
@@ -230,10 +307,10 @@
       return;
     }
 
-    var browserLanguage = getBrowserLanguage();
+    var browserTranslation = getBrowserTranslation();
 
-    if (browserLanguage) {
-      redirectToLanguage(browserLanguage);
+    if (browserTranslation) {
+      redirectToTranslation(browserTranslation);
     }
   }