OK, genuine non April Fool post this time.
What is the S Wales pronunciation of Llyn (for lake)?
I'm ok with the N Wales pronunciation from school-boy general knowledge:
Lake, llyn, loch, lough
However, for some reason, in S. Wales, my mind is telling me to pronounce Glan Llyn (*Edit Lakeside - I think) as Glan Lleen. OK probably wrong as we don't say Gleen or Breen for glyn and bryn. It's just that Glan Llinn doesn't seem to flow, if you get my drift.