The Irish language chorus -which negrosoft85 tried to render phonetically - is properly spelled:
'Sé mo laoch, mo ghille mear,
'Sé mo Shaesar, gille mear!
Ní bhfuaireas féin aon tsuan ar séan,
Ó chuaigh i gcéin mo ghille mear!

If you search the archives - I used "mear" as my keyword - you'll find several other relevant threads. Including ... mo ghile mear
It's okay to write "giolla" as that would be the nearest present day Irish equivalent of "gille", a lad. It's more common to nowadays to use "gile", brightness, in transcribing the lyrics, though that's a feminine noun so it would normally be "gile mhear". Other forums have had long debates about gile vs gille. The word/spelling "gille" is still found in contemporary Scottish Gaelic.