Usually language code is constructed like es_ES or fr_FR. However in some servers, usually on linux box, the server locale code need explicitly add .utf8. So if you have problem with strange characters where utf8 doesn’t work. Do the following steps:

1) rename the language folder, add .utf8.

/lang/es_ES.utf8
/lang/fr_FR.utf8

2) language switching also need to be modified to:

http://www.nicecoder.com/testrial/upload/set_language.php?lang_id=es_ES.utf8&back=/testrial/upload/

Notice that it is now become lang_id=es_ES.utf8.