Re: English opinion on German names
As a slang word for Germans, it is pretty old (and also has a negative connotation). People my age (early 30s) would recognize it, but would be very unlikely to use it. Younger people might not recognize it. If you named a baby this now, it is unlikely that their peers would think of it as an epithet.
I understand that re: Lion. Fine in Germany, mispronounced in the Anglosphere.
Also, since I have seen your concerns about Willy in some other comments, yes "willy" can mean penis. I think it is more common in the UK and possible the other Commonwealth countries than in the US. Here it comes across as very childish slang. An adult wouldn't use it unless they are joking around by intentionally being childish or something, but they might wonder why you would use Willy rather than Will or the full name because of the slang. It would sound a little funny to me if someone introduced themself as "Willy."