I am beginning to think that there is no way someone learning Irish could ever sound really natural unless they learned everything completely in one dialect. And I am not sure how different dialects ever understand each other when some words are totally different, lenition and eclipsis can be different, and pronunciations can be different. Anyway, thank you for your answers, I guess I can stick to my original pronunciation of mná but at least I'll now know mn-raw is the same word.
Sounding really natural requires quite advanced knowledge of a language, and yes, it will only be really natural if it matches a single existing dialect. Basically, you achieve this level when living for a while where the language is spoken, and then you learn the local dialect. This isn't only true for Irish, but maybe it's more prominent for learners of Irish because in other languages you have a dominating standard language and hardly ever learn anything about the dialects that people really use.
Learning to understand other dialects, on the other hand, isn't that hard in comparison. Even though the differences between them are often stressed, in fact they are much more similar to each other than dialects of other languages like German. It's mostly just a different accent and a few new words - but then, you also manage to understand speakers of American English, British English and Irish English, even though there are notable dialectal differences between them.
So if you keep going, I think the latter will automatically come to you sooner or later. The former, probably not so much while you're living outside of Ireland, but sounding 100% natural isn't really necessary to be able to use the language.
Well that is definitely true. I don't really expect to ever need to speak Irish but I would like to be able to read it and understand it . (Although I would be so pleased with myself if I could ever figure out how to say "sister" and "brother", lol. I listen to them and try but can't seem to make the sounds. )
"The women" is a definite noun, and "oil" is an indefinite noun. English is just a bit weird in the way it differentiates between definite and indefinite in this kind of sentence. If the Irish sentence used the indefinite mná (tá mná ar an gcathaoir) the default English translation would be "There are women on the chair".