Gaelic only has 18 letters (and W isn't one of them) but the vowels have diacritics - grave accents - that mark them as being longer.
This makes some things a bit of a nightmare because words can have different meanings based on those sounds, and that can drastically alter things. "Fèis" - "faaysh" - means "festival", "feis" with a short vowel is not a word you'd use in polite company.