Hi there @LightSideMoon! Resident Scotsman here. If you're looking for a Scottish Celtic/Pictish adjacent culture, I would reccomend looking at the Caeren Ailor culture found here: https://wiki.massivecraft.com/Caeren The Dunbrae are also very important to their identity (being a Strathclyde adjacent culture), so I reccomend you give them a look too: https://wiki.massivecraft.com/Dunbrae There is also an Irish Celtic adjacent culture, if that tickles your fancy. You can read more of it here: https://wiki.massivecraft.com/Ériunin I'm afraid, however, you won't find any elven race with Celtic connections. If you need any help with any of it, feel free to get in touch.
Fantasy accent, but nothing close to anything Celtic. It'd likely be a romantic accent (closer to French, Italian, Spanish etc), but still definitely nothing like what you'd find in real world accents.
If you want some more information on the Eriunin culture i'd be happy to help you in forum DM's. Similarly, if you have questions about the Caeren or Dunbrae cultures i'd suggest you speak @Farly108 who owns a Dunbrae family.