Fada = AltGr+vowel áéíóú

ponc séimhithe = AltGr+h, then consonant ṫḃḞ srl.

en-dash = hyphen+AltGr

em-dash = hyphen+shift+AltGr

umlaut = AltGr+8, then vowel

æ = AltGr+ '

œ = AltGr+ q

þ = AltGr+ t

ð = AltGr+ d

So many class little tricks in the Irish keyboard layout.