Issue 3697 - Fall back to i18n.getUILanguage if @ui_locale isn't supported

lib/utils.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 25 matching lines @@
       };
       document.addEventListener("DOMContentLoaded", onDOMContentLoaded);
     }
     else
     {
       setTimeout(callback, 0);
     }
   },
   get appLocale()
   {
-    let locale = ext.i18n.getMessage("@@ui_locale").replace(/_/g, "-");
+    let locale = ext.i18n.getUILanguage();
     Object.defineProperty(this, "appLocale", {value: locale, enumerable: true});
     return this.appLocale;
   },
+  get readingDirection()
+  {
+    let direction = ext.i18n.getMessage("@@bidi_dir");

[kzar, 2017/08/30 11:54:09]

Shouldn't we also make use of this.readingDirection here? Otherwise I figure we
cache it but then never use the cached value.

[kzar, 2017/08/30 13:55:02]

Argh, disregard that! I see how this works now, we replace the getter with the
value.

+    if (!direction)

[kzar, 2017/08/30 11:54:09]

Nit: Please use braces since it spans multiple lines with the comment.

[Sebastian Noack, 2017/08/30 16:28:24]

I'd rather just move the comment above.

[Oleksandr, 2017/08/30 23:00:36]

Done.

+      // This fallback is only necessary for Microsoft Edge
+      direction = /^(?:ar|fa|he|ug|ur)\b/.test(this.appLocale) ? "rtl" : "ltr";

[kzar, 2017/08/30 11:54:09]

(I assume Sebastian checked this regexp, I have no idea if it's correct.)

[Sebastian Noack, 2017/08/30 16:28:24]

For reference, this is the regular expression we use on Safari:

  /^(ar|fa|he|ug|ur)(_|$)/

Using \b (end of word) instead of _|$ is correct, as we have dashes instead of
underscores here. However, I didn't check whether this covers all right-to-left
languages supported by Windows.

[Oleksandr, 2017/08/30 23:00:36]

Based on the list here:
https://msdn.microsoft.com/en-us/library/aa919356.aspx?f=255&MSPPError=-21472...
it looks like we are handling even more languages that Windows supports. So this
should be fine.

+    Object.defineProperty(
+      this,
+      "readingDirection",
+      {value: direction, enumerable: true});

[kzar, 2017/08/30 11:54:09]

Nit: Please put the closing parenthesis on the following line - same indentation
as the start of "Object" above.

+    return this.readingDirection;
+  },
   generateChecksum(lines)
   {
     // We cannot calculate MD5 checksums yet :-(
     return null;
   },
   checkLocalePrefixMatch(prefixes)
   {
     if (!prefixes)
       return null;
 
@@ skipping 50 matching lines @@
   {
     let docLink = require("prefs").Prefs.documentation_link;
     return docLink.replace(/%LINK%/g, linkID)
                   .replace(/%LANG%/g, Utils.appLocale);
   },
 
   yield()
   {
   }
 };