The song "Tír na nÓg", like many of the Celtic Woman songs, is partly in English and partly in Irish Gaelic. Unlike many of those Celtic Woman songs, this one doesn't seem to be based on a traditional Irish ballad, as far as I can tell - it may have been written specifically for Celtic Woman. This makes it difficult to find out the meaning of the lines in Gaelic, the chorus of this song.
Genius.com has the following lyrics, which are certainly what the words sound like but (knowing what Gaelic is like) almost certainly nowhere near the correct spelling:
Sha ta co ti oh scum ne rivna
Sha ta co ti oh nugga Tír na nÓg
Sha ta co ti oh scum ne rivna
Nug a Tír na nÓgKaraokeLyrics.net has the following lyrics, which look much more believable as the correct spelling for the Gaelic words that sound like the above:
Saeta-Ceatia sciamh-ne riabhanach
Saeta-Ceatia nuige Tír na nÓg
Saeta-Ceatia sciamh-ne riabhanach
Nuige, Tír na nÓgLyricsTranslate.com has the following translated lyrics, but I'm unsure of the source for this translation:
Yes, Who is it?
Yes, who took tea from the land of the young?
Yes, Who is it?
Nave from Land
Putting the words from KaraokeLyrics.net (the most believable Gaelic spelling) into Google Translate, it recognises them as Irish but doesn't provide any English translation. Trying a single word gives the translation "zebra", which doesn't seem believable.
Tír na nÓg itself is of course the Irish name for the Celtic Otherworld, but that only gives us a few words of the chorus and potentially hints at the overall meaning.
How are the words of this Gaelic chorus really spelled, and what is their meaning? Looking for believable sources, such as the people who wrote/produced this song (assuming it isn't a traditional one) or a native/fluent speaker of Irish Gaelic.