"Invalid Characters" error message translation is missing

[russCloak]

Minor issue, just figured it would be better to have it tracked.

When filling out the sign up form with invalid characters (Ü for instance) you get the following:

[jurre]

Thanks!

[jurre]

Hmm, this is strange because in config/locales/en.yml we have:

  account:
    invalid_characters: "contains invalid characters"

[michalsz]

This is read on #326