English versions of Polish given names

Had a Polish neighbor named Wladyslaw aka Wladek, and he preferred
to be called by his American name Wally!!

Always figured it was short or familiar for Wallace, not Walter.

I know a guy whose Polish first name is "Wieslaw," but he wants to be called "Walter." Wondering why not "Wesley."

Probably, he doesn't know such a name exists, or it sounds too close to 'weasel' for his comfort.

Why not keep Wiesław?

He lives in the US and pronouncing Wieslaw to people would be difficult and meaningless. "Wieslaw" is also his name a drivers license. It's just easier to live in the community I guess.