Kinda like Italian and French, they often avoid hiatuses (vowels coming together) by using different prepositions or possessive pronouns (sa amie becomes son amie, a un becomes ad un), or élision (la art becomes l'art, il uomo becomes l'uomo). Simply put, they avoid what I call "uncomfortable letter combos".
The single most common word pair in Irish is Tá an.
Irish has absolutely no problem with "vowels coming together" - the language is full of such examples. There are places where "clashing vowels" have traditionally been avoided, but they are actually the exception, rather than the rule.
Irish keeps amazing me every day :) Under : https://en.m.wikipedia.org/wiki/Irish_initial_mutations#Changes_to_vowel-initial_words, scroll down to “Otherwise, there is the prothetic onset h…”. I think that's it
And thank you very much galaxyrocker for all your useful comments ! :)