Tolkien said he didn't particularly like the Gaelic language so I don't think it would have provided the basis for any of his own languages. I found a quote in his letters written in 1955 where he says that he finds "both Gaelic and the air of Ireland wholly alien - though the latter (not the language) is attractive." he also wrote in 1967 "I have no liking at all for Gaelic from old Irish downwards, as a language". But he admitted that it was of great philological interest so he has studied it. The word nazg (ring) in the Black speech, he wrote, is probably derived from the Gaelic word nasc (in Scottish usually written: nasg) which has the same meaning. However, he says it wasn't done intentionaly.
I think the Shire was based quite simply on the rural England where he lived with his brother and his mother before her death (Warwickshire to be precise). Indeed, a lot of the place names in rural England end in shire. In rural England people drink ale from pubs also and use the terms lad and lassie. The term lad is common all over Ireland and Britain as a whole. The term lassie is mainly Scottish and colleen (from Gaelic cailėn is more common in Ireland.
Taking Middle-earth as a whole, Tolkien said that all the history is "supposed to take place in a period of the actual Old World of this planet". He wrote that the name "is just a use of Middle English middel-erde (or erthe), altered from Old English Middangeard: the name of the inhabited lands of Men 'between the seas'".
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"Come away, O human child!/ To the waters and the wild/With a faery hand in hand,/ For the world's more full of weeping than you can understand."
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