Update index.js

src/runtime/web/index.js

@@ -25,7 +25,15 @@ documentReady().then(() => {
 });
 
 function createLocalization(name, resIds, defaultLang, availableLangs) {
-  function requestBundles(requestedLangs = new Set(navigator.languages)) {
+  let langs = navigator.languages;
+
+  for (let i=0; i < langs.length; i++) {
+    if (langs[i].indexOf('-') > 0 && availableLangs.has(langs[i]) === false) {
+      langs[i] = langs[i].substring(0, langs[i].indexOf('-'));
+    }
+  }
+
+  function requestBundles(requestedLangs = new Set(langs)) {
     const newLangs = prioritizeLocales(
       defaultLang, availableLangs, requestedLangs
     );