You need to look inside gtranslate.php file. You can search for Select Language and translate it to your language. After you save it, make sure to re-configure and save the GTranslate module in your wordpress back-end.
You need to make sure to reconfigure the GTranslate from the settings, so the widget code is re-generated. You may try to delete the widget code, change some settings and see that it is being re-generated.