[Backport to 11.0] Default Wicket validation messages do not use Chinese locale

To reproduce:

• In the login screen, switch to the Chinese language
• Leave all other fields empty
• Click the button

Expected: a fully Chinese error message
Actual: part of the error message is still English

This is most likely due to the usage of some of the built-in Wicket validators that do not pick up the locale that is used by the CMS.