Non-default custom String-Translator?

[Onno Scheffers]

 Is there a way I can setup a custom String validator that is only added to
fields I explicitly set the translator for?

I want to make sure some TextFields (username and email-address) are
converted to lowercase Strings. I figured a Translator would be useful for
that. But when I create a LowercaseTranslator using the name 'lowercase' all
TextFields in the application seem to use the LowercaseTranslator all of a
sudden.

This is how I contributed my Translator:

   public static void contributeTranslatorSource(Configuration<Translator>
configuration) {
      configuration.add(new LowercaseTranslator());
   }

regards,

Onno