Translate field name displayed within validation error messages?
Craft/Yii sees that string as:

'{attribute} cannot be blank.' =&gt; '{attribute} darf nicht leer sein.',


Where {attribute} is the dynamic part - in this case your field handle.

If I'm understanding your question correctly, there isn't a way to translate that field handle in this context because you're in charge of what it's called to begin with.

I would assume, for example, if you're using the German locale, that you would already have a German context field handle name in place already.