Form component's validate parameter cause excpetions when clients use zh-cn language

[Fight Ice]

When the client web browser use the zh_cn locale to load my login page, i get a 
exception like this :
Render queue error in BeginRender[admin/Login:username]: d != java.lang.String

but if client use the en locale, it works correctly.
if i want to use zh_cn locale to load my login page, i found that if i use 
minlength validator and other similar validators, i'll get exceptions.

Login.java(partial)

    @Persist
    @Property
    private String userName;
    
    @Property
    private String password;

Login.tml(partial)

    <t:form t:id="loginForm">
        <t:errors/>
        <t:label for="userName"/>
        <t:TextField t:id="userName" t:validate="required, minlength=6" 
size="30"/>
        <br/>
        <t:label for="password"/>
        <t:PasswordField t:id="password" t:validate="required, minlength=6" 
size="30"/>
        <br/>
        <input type="submit" value="Login"/>
    </t:form>

If i just use required validator, it works.