Scottish vs Irish: two Celtic-influenced varieties
Both Scottish and Irish English developed in close contact with Celtic languages — Scots Gaelic in Scotland, Irish Gaelic in Ireland. Both retained rhoticity that other British Isles varieties lost. But the vowel systems are very different: Scottish English uses the Scottish Vowel Length Rule (vowel length depends on the following consonant), the rounded LOT vowel, and a much wider use of trilled /r/. Irish English has a more melodic intonation and the famous t/d substitution for th.
