What I want to do is put app-text/acroread -linguas_ja in portage.use to work around bug #97401. But this doesn't work; apparently the LINGUAS variable takes precidence (so I still get the Japanese acroread). So there needs to be some way to set LINGUAS for an individual package. Just doing env LINGUAS=en emerge acroread is error prone (it would be lost next time a new version is available and in any case won't really work for me because I have a dialup at home, so I generate a list of files to download and get them elsewhere).
*** This bug has been marked as a duplicate of 44796 ***