(In German) No, it's not controversial at all. The nationality of the author has nothing to do with the nationality of the character.
10 seconds sound clip from the Inglourious Basterds movie soundboard.
You can hear this line at 01:12:24 in the Blu-ray version of the movie.
Quote context
[...]
- Look, she's not a military strategist. She's just an actress.
- You don't got to be Stonewall Jackson to know you don't want to fight in a basement.
- She wasn't picking a place to fight. She was picking a place isolated and without Germans.
- Schnapps? Schnapps? Schnapps... Schnapps... Schnapps... Five schnapps, please.
(In German) If I had a wife, would she be called a squaw?
(In German) Is my blood brother Old Shatterhand?
(In German) Did Karl May write me?
[...]