I wonder if there's a site out there that could help me with my minor Welsh character. He hasn't much of a speaking part but I want to get it right.
Just append -bach occasionally to people's names, you'll be fine
Seriously, I'm a little concerned about this myself. For a WIP I have people from Wales, Cornwall, Ireland, Man, and highland and lowland Scotland speaking English together, and I'm trying to give them distinctive voices, despite not being a native of the UK myself.
Broad Scots is easy enough -- so easy you can fall into a parody if you're not careful -- but some of the others are less clear, especially if you don't use dialect-spellings. There are plenty of sites out there including various Wikipedia pages that list characteristic phrases and styles, but the trick is to use them in a way that suggests the differences without seeming blatant or intrusive. So for example, I gather that in Wales there is more of a tendency to phrase statements as questions than in England. But this tendency can't be presented in too obvious a way or it will look silly, don't you think?