How i for new users dont use for Username area *-/@#%$ all symbols and cyrillic symbols.
For Username area use A-z, a-z and 0-9 symbols.
And Accaunt page add Name and Surname area use all symbols.
Twitter user page example.
You'll need a filter plugin: http://www.question2answer.org/modules.php?module=filter
Add the function filter_handle(&$handle, $olduser)
Then check whether $handle is of the format you want.
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