added comment for a languages definition

tracim/tracim/public/assets/js/trad.js

 
 function __ (tradId) {
   const normalizedLang = (() => {
-    switch (globalTracimLang) { // this var is set in tracim header
+    switch (globalTracimLang) { // @TODO - Côme - 2017/10/30 - need a more secure way to handle different langs
       case 'fr':
       case 'fr-fr':
       case 'fr_FR':