In this post, I discussed whether to decline German adjectives when you use them in an English sentence. I don’t, but here’s somebody doing it on the Wikipedia page for Leo von König:
He was not well thought of by Adolf Hitler, however, and his works were removed from the “Großen Deutschen Kunstausstellung” at the Haus der Kunst in 1937.
Had I written that sentence, it would say: …his works were removed from the “Große Deutsche Kunstausstellung” at the Haus der Kunst in 1937.
So there!
I agree with you. The phrasing suggests poor German knowledge on the part of the Wikipedia editor.