Item 6 in http://gtranslate.net/forum/troubleshooting-gtranslate-pro-t368.html says:
6. When I select a language I'm being redirected to a URL with the language code, but I still can see the original language.
- Enable debug: define('DEBUG', true); in gtranslate/config.php, delete cache/limit.txt if it exists and refresh the page. After that you will see a debug.txt file inside gtranslate folder, where you will see the communication between your server and google translator. Check the request URL for a translation and the response. If you have reached the daily limit for your API key you need to wait. If you get a Bad Request then the API key is incorrect.
Yet in plugins/system/gtranslate folder, I can't find any config.php! Could you advise me please?