Gaulish was an ancient Celtic language that was spoken in parts of Europe before and during the period of the Roman Empire. In the narrow sense, Gaulish was the language spoken by the Celtic inhabitants of Gaul (modern France, Belgium and Northern Italy).Gaulish is a bit of reconstructed,but enough to write a song :)

A beautiful druid language, here is a song in reconstructed Gaulish:

Song's name is "Omnos" which means "Fear".If you are interested, the band Eluveitie have many songs in Gaulish, both metal and acoustic.