I recently had to put up with a satellite navigation system mispronouncing around 90% of place names. The (mis)pronunciations were clearly based on spelling,

I recently had to put up with a satellite navigation system mispronouncing around 90% of place names. The (mis)pronunciations were clearly based on spelling, but the system developers weren't trying very hard, or didn't know the spelling-sound correspondences or how to encode them. A rule-based approach would get it right most of the time, and exceptions can be handled by table look-up. (Obviously you check whether it's an exception first before applying rules.) I've done this before, for words rather than place names.