use fluent-langneg for subtag support

server/languages.js

@@ -4,11 +4,9 @@ const fs = require('fs');
 const path = require('path');
 
 function allLangs() {
-  const langs = fs.readdirSync(
+  return fs.readdirSync(
     path.join(__dirname, '..', 'dist', 'public', 'locales')
   );
-  langs.unshift('en-US'); // default first, TODO change for fluent-langneg
-  return langs;
 }
 
 if (config.l10n_dev) {