Most of the foreign places which have acquired English names seem to places of particular significance - major cities and seaports. Most of these seem to be simply mispronunciations of the native names - it is easy to see how "Firenze" might mutate into "Florence" in an English mouth, especially when it's been passed around a few times. Once it gets written down, that name tends to stick.

We should also remember that the modern pronunciation in the foreign language may have altered from the time the English version was adopted. Was the "s" in Paris sounded in mediaeval French?

I grew up in Essex not far from Billericay (Bill-er-ICK-ee, although the "ck" is usually replaced by a glottal stop these days), famous as one of the gathering places of the Pilgrim Fathers before joining the Mayflower. When they arrived in Massachusetts, they named a settlement there "Billerica" - reflecting its 17th Century spelling and pronunciation. These things aren't fixed.