This gets asked for from time to time; texts have been posted at least twice, and are quite easily found by typing, for example, for ireland i into the best of several search engines which are available on this site, the "Digitrad and Forum Search".  You will find it on the main Forum Page.  Here is another posting of Gaelic text:

For Ireland I'd Not Tell Her Name

As Philippa suggests, your friend would be well advised to learn at least some of the rudiments of any language he can't speak before attempting to sing in it, but I expect you've already told him that!