Marseille!--How is it Pronounced?

[Graham Boak]

Most of the examples you quote are actually completely different names, rather than merely variations. However, I don't think this is true of Danzig/Gdansk. Here is a case of one root name with two linguistic variants, like Cologne/Koln or London/Londres.

I assume that this kind of variation is rather uncommon in any language, as few foreign city/town names would go into common usage.