I am fairly sure I know the answer on this, but for deck building and having in play purposes Eiserne Drossel and Aisel Nedrossel are considered two different cards, yes?

Yep. You can have 4 of each in your deck, and one of each in play.

In the games, they are the same.

I think it's one of those cases where Namco mis-translated their names, but as long as the names are different in the cards, they're different cards. So you can have 4 of each max in a deck.