Out of interest, are the English town names a translation of the Irish names, Completely different, or a vague English Pronunciation guide?
They're usually, but not always, an anglicised pronunciation of the Irish name. A lot of this is because the maps and records drawn up by the English who couldn't speak the language, and wrote down what they thought they heard.
Irish place names are incredibly detailed to people who do understand the language. Gort a' Choirce is literally "the field of the oats" for example (more specifically, it is refers to a field of the size someone with two oxen could plough in a day as there are many more Irish words for fields of different types), and in English, it is Gortahork, which is roughly how you pronounce Gort a' Choirce.
Dún Dealgan - Dundalk
An Dubh Linn - Dublin
Cill Chainnigh - Kilkenny
Dhún na nGall - Donegal
I've observed things like this on my cycle tours in the west of Scotland too.
Campbeltown was originally known as Ceann Loch Chille Chiarain or (Kinlochkilkerran in English) and means "Loch by the church of Ciarán." It was renamed later after Campbell, Lord of Argyll.
I am far from a language expert, but do like to look at the origins of place names.
Some are translations, some have little or no connection at all to the Irish name as the name has got changed over time. Westport does not equal Cathair na Mart, in pronounciation or meaning.