Let's not forget he's a native English speaker so the world is really his oyster. I'd love to see him play in the Netherlands or Belgium, personally
I think those leagues along with Switzerland and Austria and maybe even France would be perfect for him. Netherlands probably the best though.
One major issue he might have is visas. He's not got a Euro Passport so would need a visa to play in those other nations. Maybe he's trying to get his German passport to allow him to play across the EU visa free. A move out of Germany would ruin that.