http://www.icyphoenix.com/viewtopic.php?f=4&t=1524&p=48281#p48281
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Mighty Gorgon
Sun 14 Mar, 2010 09:59

Re: CUSTOMIZATION - Removing Restrictions On Using Some Special Characters In Username
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Unfortunately current Icy Phoenix doesn't fully support UTF-8 and special chars.

I'm working hard to the project to enhance and fix this aspect, so you should wait the next version to have a new try with special chars usernames.