Willy etc - better to go with
Will or
William
Fritz - not great ("on the fritz" means something isn't working consistently), but not awful. I think it's pretty associated with German-speakers
Bent,
Bente -
Bent just doesn't sound very name-y. It could be viewed as slang, but not slang that young people would use in the US. I can't speak for other countries. People wouldn't know how to pronounce
Bente at all.
Fanny - I'd avoid it, especially in the UK or areas that use more UK slang. In the US it still isn't great.
Lion - people will assume it is pronounced like the animal, so if you want it pronounced right I'd spell it
Leon
Arian - too close to
Aryan to work well in the US and probably Canada (again I can't speak for other areas), but if you can spell it in a way to get the first A to sound like "ah/aw" it would be ok.
Christian - fine, just likely to be pronounced the same way we pronounce the word in our countries.