its actually quite hard to tell someone how to pronounce the placenames through typing.
Welsh placenames nearly allways actually mean something, and very rarely does the English Translation given on Road signs n some cases reflect what the welsh actually means.
my town Aberystwyth for instance translates as, the Mouth of the River Ystwyth, and there is no "english" version in usage.
Aberteifi further south would appear on Maps as Cardigan, but Aberteifi translates as Mouth of the River Teifi, or just outside my town, Llanbadarn Fawr, translates as the Village of Badarn's Church. the only example of the English following the welsh that i can think of is Newtown, Powys, which in Welsh is Y Dre Newydd, literally the New Town. Llanbedr Pont Steffan is given on maps and signs as Lampeter, but the translation is something like Bedr's Church, Steffan's Bridge.
Some of the wierd english versions are simply due to the English Invaders in medieval times being unable to pronounce them. I live in Aberystwyth, County of Ceredigion, Ceredigion means the Kingdom of Ceredig, and dates back to the 4th century. Some important english guy, was unable to pronounce this, and it came out something like Cardigan, hence the town of Cardigan, and the former county of Cardiganshire.
many welsh place names actually predate England not just as an area or concept, but literally from before the first Saxons arrived, as i recall Ceredig was given his kingdom by the Romans, so long before any saxons were ever seen.
some Welsh, especially a few of the words which precede a name are corrupted versions of Latin, such as Caer (fort) or Bont (bridge)
Sorry for the History lesson lol

For some interesting long welsh place names theres:
Llanfihangel-yr-Creuddyn, and Llanfairpwllgwyngyllgogerychwyrndrobwllllantysilio gogogoch (i am not joking),