Oh, you can use
Oscar in Germany (would spell it
Oskar though). I'll try to explain why I wouldn't because this is a general phenomenom for me: The same name (usuable in both countries) has a different feel to me in
German or in English. Sometimes it's just that I prefer one pronunciation but
Oskar in
German and
Oscar in English are almost pronounced the same. I guess it must be about naming trends: While
Oscar feels very ready for a comeback in the US and just so stylish,
Oskar in Germany is a little dated and nothing special. They're just totally different names to me depending on where they are used. Does that make any sense?