Hi there,
I am wanting a small Gaelic translated quote from Yeats' play Cathleen Ni Houlihan tattooed above my knee however I wanted to be certain of the translation beforehand.

The quote is "My four beautiful green fields"

I'm also really curious as to what this would be in old Irish if anyone knows.

Any help at all with this would be amazing and would really be greatly appreciated. Thank you so much.

I think either of these would work:

Mo cheithre pháirc ghlasa álainn.

Mo cheithre páirceanna glasa álainn.

They mean the same thing but just different grammatical focus.

The problem for me is "field". There are a few ways to say it depending on meaning and dialect.
Let's wait to see what someone else suggests before you commit to ink.

Mo cheithre pháirc ghlasa áille

Plural of glas and álainn is necessary (at least in Standard Irish): áille

I thought so, too, but isn't "páirc" considered a weak plural? And wouldn't "álainn" be used?

Páirc is singular.
Its plural is páirceanna.
You use singular of nouns with numbers (>1), but always plural of adjectives:

cheithre pháirc/theach/bhórd áille


Outside of numbers:
It doesn't matter wether there's a weak or strong plural in nominative case:
You use plural adjective forms with plural nouns:
an fear álainn -> na fir áille
an pháirc álainn -> na páirceanna áille

Except in genitive:
A "weak genitive plural" form of the adjective (= nominative singular) is used with weak genitive plural forms of nouns:
pictiúr na bhfear álainn.
but
pictiúr na bpáirceanna áille

OK, thank you very much for your explanation.
Tim