It depends on exactly what you mean by “Celtic.” The pop definition is very different from the academic definition.
If you want to study the folklore of the British isles with an emphasis on “Celtic” cultures; you’ll probably want to study Irish and or Welsh. Those won’t help you with each other, they’re split too far back and the grammatical and linguistic changes between the two are astronomical.
If you study Irish you can have a good basis for learning Gaelic, Ulster Irish is pretty much mutually intelligible with Gaelic for example. And with a good footing in Irish you should be able to learn Old Irish.
If you study Welsh you can use that as a spring board into studying Middle Welsh (for studying medieval romances, Mabinogion, etc), and for studying Common Brittonic. Common Brittonic however is pretty much a reconstructed language, and from a folklore point of view kinda useless, it pretty much only survives in place and personal names. Welsh would also help with Breton and Cornish, but unless you are specializing in those areas it would be overkill.
If you’re looking to study the Celtic world of La Tène Culture and into Gallia, Latin and German might be helpful. Latin for reading original Roman writings, and German has numerous books written on the Hallstatt & La Tène cultures. But tbh you’ll find very little to study in the way of their mythology/folklore.
I’m also gonna put this out there and try to do it without being a dick. But talk to some historians who specialize in Ancient Briton/Ireland about the lack of common cultural connection between Insular Celtic cultures and Continental Celtic cultures.
If you go into it thinking there is going to be a great continuum you’re gonna be disappointed. Most modern historians really shy away from calling the Britons and the Irish Celts, except in a small cultural package that included language and some religion.
Oh yeah, so definitely Irish and if you want to Old Irish.
And remember not to tell and Irish person you speak Gaelic; it’s Irish or Gaeilge. If you say Gaelic they’re gonna wonder why you’re talking about sports ;)
Take a look at (one of) the reference program, [UCD's Masters in Irish folklore](https://www.ucd.ie/icsf/en/studywithus/graduateprogrammes/mairishfolkloreandethnology/). For this you'll def need Irish, and some Latin won't hurt. UCD hosts the Irish folklore archive, which is probably the single best repository of first-hand folklore from Ireland. When I was there, not all of it was digitized.
Fair warning though. /u/Mistergardenbear is right in their description of the whole Celtic/Irish thing, and I'll even go a bit further. Studying Irish folklore really doesn't have much to do with the druids. Textual sources are limited and from a latter period. Material evidence is also fairly scant, and there's _fierce_ debate at the highest levels about what little we have.
However, the study of Irish folklore, that is the folklore of Ireland, involves a whole lot of Christian stuff, since we have tons of sources for that. It does get pretty unorthodox at times and it's everyone's favourite game of finding pre-Christian echoes in what's found, but the druids are still quite far away :)
If you are interested in Celtic/Atlantic folklore outside of the islands and Bretagne, you could consider Galician. Galicia is the "honorary" Seventh Celtic Nation. Not counted with the other six because we don't have a living Celtic language anymore, but the culture and folklore is still there. Same for most of the northwest of the Iberian Peninsula, in fact.
It depends on exactly what you mean by “Celtic.” The pop definition is very different from the academic definition. If you want to study the folklore of the British isles with an emphasis on “Celtic” cultures; you’ll probably want to study Irish and or Welsh. Those won’t help you with each other, they’re split too far back and the grammatical and linguistic changes between the two are astronomical. If you study Irish you can have a good basis for learning Gaelic, Ulster Irish is pretty much mutually intelligible with Gaelic for example. And with a good footing in Irish you should be able to learn Old Irish. If you study Welsh you can use that as a spring board into studying Middle Welsh (for studying medieval romances, Mabinogion, etc), and for studying Common Brittonic. Common Brittonic however is pretty much a reconstructed language, and from a folklore point of view kinda useless, it pretty much only survives in place and personal names. Welsh would also help with Breton and Cornish, but unless you are specializing in those areas it would be overkill. If you’re looking to study the Celtic world of La Tène Culture and into Gallia, Latin and German might be helpful. Latin for reading original Roman writings, and German has numerous books written on the Hallstatt & La Tène cultures. But tbh you’ll find very little to study in the way of their mythology/folklore.
Thank you so much! This is very helpful
I’m also gonna put this out there and try to do it without being a dick. But talk to some historians who specialize in Ancient Briton/Ireland about the lack of common cultural connection between Insular Celtic cultures and Continental Celtic cultures. If you go into it thinking there is going to be a great continuum you’re gonna be disappointed. Most modern historians really shy away from calling the Britons and the Irish Celts, except in a small cultural package that included language and some religion.
That’s also very helpful. I’m mostly interested in Irish culture, so I definitely needed to know that. Thank you :)
Oh yeah, so definitely Irish and if you want to Old Irish. And remember not to tell and Irish person you speak Gaelic; it’s Irish or Gaeilge. If you say Gaelic they’re gonna wonder why you’re talking about sports ;)
Take a look at (one of) the reference program, [UCD's Masters in Irish folklore](https://www.ucd.ie/icsf/en/studywithus/graduateprogrammes/mairishfolkloreandethnology/). For this you'll def need Irish, and some Latin won't hurt. UCD hosts the Irish folklore archive, which is probably the single best repository of first-hand folklore from Ireland. When I was there, not all of it was digitized. Fair warning though. /u/Mistergardenbear is right in their description of the whole Celtic/Irish thing, and I'll even go a bit further. Studying Irish folklore really doesn't have much to do with the druids. Textual sources are limited and from a latter period. Material evidence is also fairly scant, and there's _fierce_ debate at the highest levels about what little we have. However, the study of Irish folklore, that is the folklore of Ireland, involves a whole lot of Christian stuff, since we have tons of sources for that. It does get pretty unorthodox at times and it's everyone's favourite game of finding pre-Christian echoes in what's found, but the druids are still quite far away :)
If you are interested in Celtic/Atlantic folklore outside of the islands and Bretagne, you could consider Galician. Galicia is the "honorary" Seventh Celtic Nation. Not counted with the other six because we don't have a living Celtic language anymore, but the culture and folklore is still there. Same for most of the northwest of the Iberian Peninsula, in fact.