Czech translation and mb_language error

Hi!

I was trying to install RounCube Webmail which is wonderfull. I installed it from FreeBSD ports and works fine, but when I try in preferrences set up Czech language, it's switch off to Czech (just this screen) and wrote php error mb_language 'cz' is not supported.

I would like to try if there's not a mistake, because country code is ususally 'cz' but languague code is 'cs' or 'cs_CZ'. I was trying to change an array in program/localization/index.inc.php but in the settings form is still 'cz'.

Could you help me or just destinate me where could be the problem...

Sincerely

Miroslav Koula