As Baile Letras

The song itself is all intonation,
Although you might say the intonation
Is "based" in Irish Gaelic.
Enya sings "oró, horo, mo-ray he u way, he u way"
And so on.
The word "oró" is an interjection
that could be translated as "oh!" or "oho!",
But the rest of the song is intonation.

Information from Louise Ní Fharrachair and Daniel Quinlan