I worked in both Port Talbot and Cardiff. Both had different local accents and dialects. I added an extra one!
The villages around Llanelli have some differences too. Gwendraeth valley has some of its own compared to Llanelli town.
I had an uncle who was a vicar in North Wales. His Welsh was different to both the North and South Wales variants. He did have a Gog (N Wales ) accent. Some of his Welsh words were so long you forgot how they started by the time he got to the end! He was also very Dywiol that is spoke with a musical lilt in a soft tone. When he retired he moved to Aberwristwatch on the West coast ( look it up on a map

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Sospan jnr went to Uni in Cardiff. Stayed there ever since. His accent varies depending on the company he is with. Local Cardiff to BBC Wales to home here in Llanelli. He did a 4 program series for TV about going to Naples for the pizza world championships ( he has a pizza business). One episode was based in Bardi and showed the very strong links to Wales. There are many from that area who moved to Wales and several could speak Welsh. The series is on BBC Wales. Bois y Pizza.
A few years ago we went to Brittany a few times. Welsh and Breton have many similarities so my combination of Welsh and O-Level French made it easier to talk with locals.