Captcha Error – Need help

Hello,
We found some kind of “bug”, at the registration-page. Every section of it works, till the Captcha.
You can write the correct captcha, but there comes a error message:”Invalid captcha.” We don’t know what
to do and need some help.

http://onlygames-community.eu/user-registration/

Incidentally, we have a German/English Community and it would be great if you could show us how we can
edit the Website, so you can change the language on yourselfe as visitor.