Eluveitie

Catoues caletoi
Urit namantas anrimius
Ro- te isarnilin -urextont,
Au glannabi rhenus
Ad ardus alpon,
Tou' magisa matua

Tou' brigas iuerilonas

—Slania's Song

Eluveitie are a Swiss Folk Metal band. Eluveitie blends elements of Melodic Death Metal with celtic folk music, all with a pagan theme. As far as folk metal bands go, they are a fairly well known and well established act, having released 4 full length studio albums since 2006. One of them, Slania (2008) charted in Switzerland and Germany.

Eluveitie provides examples of the following tropes:

Celtic Mythology
Everything's Louder with Bagpipes
Gratuitous Foreign Language - The page quote is an example.
Heavy Mithril
Indecipherable Lyrics - Unless of course you speak the dead language Gaulish, which Eluveitie uses for some lyrics.
Neoclassical Punk Zydeco Rockabilly - as is the case with most folk metal bands.
New Sound Album - Evocation I: The Arcane Dominion was the band's first acoustic album, ditching the metal for almost pure folk music.