"IRN BRU is not from Islay."
Translation:Chan eil IRN BRU à Ìle.
If the vowel is is either long sound or if it takes stress, then use the modern acute. The language has been through several spelling reforms, and, it is now much more simplified. The only one that is tricky is the diphthong 'eu' as in Seumas which is, for all intense and purposes, a very similar vowel sound to the Irish way of spelling the name, inclusive of the 'fada'. Sorry, I doubt this helps. Think of the Anglicised Hamish, which, is derived from Seumas in the vocative, "Tapadh leat, a Sheumais".