Can we force members not to use a language as username?

Hello again,

I have a quick question. Since I have integrated joomla databases with other systems, I have to ask my members not to use farsi language and space in their username, but some people are careless about notifications. Is there any way we force them to stick to english and receive an Ajax error if they use farsi charterer?

Thanks,

I found it myself. Under validation of username. Pretty cool.