Just for reference, I’m using my Hearth culture’s spelling and pronunciation for ‘Beltane’ or May Day. The literal translation for this word is ‘May Day’ in my Green dictionary. I’ve also seen it spelled ‘Bealtuinn’, although I can’t substantiate that; it’s not in my dictionary.
Bealltainn is pronounced ‘byaul-tinn’, with emphasis on the first syllable, as is usual in Gàidhlig. The ‘tinn’ part would have a very, very soft ‘t’, not like a hard American ‘t’; more like a voiceless ‘chi’ in ‘church’. Emphasis is always on the first syllable, unless there is an accent mark saying otherwise.