What I've seen is that none of the language packs have 100% translation! I've found the solution, just follow these steps:
1) Take off the language button from http://www.example/my/admin/languages/mod/
2)Use a third party language button like Google Translate, it works better! http://translate.google.com/translate_tools?hl=en
3) Customize the widget any way you want!
4) Copy the widget code from http://translate.google.com/translate_tools?hl=en
5) Paste the code in Custom head code or Custom tail code located here: http://www.example.com/my/admin/settings/page
Then your good to go!
Hope this helps and this is what I use on my site! It works 100% better!