Issue 5860 - options page is broken in test enviroment

ext/common.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 65 matching lines @@
       if ("_extWrapper" in listener)
         window.removeEventListener("message", listener._extWrapper, false);
     }
   };
 
   /* I18n */
 
   let getLocaleCandidates = function(selectedLocale)
   {
     let candidates = [];
-    let defaultLocale = "en-US";
+    let defaultLocale = "en_US";
 
-    // e.g. "ja-jp-mac" -> "ja-JP", note that the part after the second
+    // e.g. "ja-jp-mac" -> "ja_JP", note that the part after the second
     // dash is dropped, since we only support language and region
     let parts = selectedLocale.split("-");
     let language = parts[0];
     let region = (parts[1] || "").toUpperCase();
 
     if (region)
-      candidates.push(language + "-" + region);
+      candidates.push(language + "_" + region);
 
     candidates.push(language);
 
     if (candidates.indexOf(defaultLocale) == -1)
       candidates.push(defaultLocale);
 
     return candidates;
   };
 
   let selectedLocale = window.navigator.language;
@@ skipping 82 matching lines @@
         if (locales.length == 0)
           return "";
 
         let locale = locales.shift();
         readCatalog(locale, "common.json");
         readCatalog(locale, catalogFile);
       }
     }
   };
 }());