Can't import translations if target language has uppercase letters

Some language codes look like "en-CA", "en-US", etc. If I perform a translation import and I put such language codes in the list of languages (which ends up stored in $options['translate_languages']), the import will fail with You can use only existing and enabled languages and not "!languages". That's because the module (for some reason) calls drupal_strtolower on $options['translate_languages'], which causes the input language codes to no longer match those in the system, throwing the above error. This patch removes the call to drupal_strtolower.