Amon Amarth encouraged fans at a festival to sing along even if they don't know the lyrics: "It's death metal, no one would tell the difference!"
But by the way their lyrics are in plain English and make as much sense as you can reasonably expect from a rock band, and vocal style is on the more comprehensible end of death metal spectrum.
Amon Amarth really isn't a good example, because many of their songs have perfectly comprehensible lyrics, even by people who perhaps aren't native English speakers (which the band themselves aren't)
But by the way their lyrics are in plain English and make as much sense as you can reasonably expect from a rock band, and vocal style is on the more comprehensible end of death metal spectrum.