In my Picard preference, I have the "translate artist names" checked, and English choosen.
If I try to tag a release whose artist has english aliases, it takes the first one and not the primary one.
For instance, for Moby : http://musicbrainz.org/artist/8970d868-0723-483b-a75b-51088913d3d4/aliases
Picard will try to tag with "DJ Moby" and not "Moby" which is the primary.