User name in membership in other language?

I'm create a membership feature in asp.net. However, this website will be in other language in stead of English. In user name field, it has regular expression validator that doesn't allow other symbols in stead of english alpha beta. My question is that if I remove the validator, it should allow input other language, is this right? if so. The user name should consider as unique field? Thanks,
<asp:TextBox ID="UserName" Runat="server" Height="18px" Width="175px"></asp:TextBox> <asp:RequiredFieldValidator ID="UserNameRequired" Runat="server" ControlToValidate="UserName" Display="Dynamic" ErrorMessage="user name required" ToolTip ...