AFAIR, needs directives on the server side.
LyX pretends that the server name is none of my business :-(
If it's Apache, language negotiation may be on by default:
but the mechanism does not seem compatible with pmwiki, as it requires
pages in different languages to have suffices like .fr, .de, etc.
I guess that this was the problem that raised objections from you at the
time. Forget about my suggestion.
I think something can still be done. It's a matter of modifying the pmwiki
code to direct pages differently depending on the user's chosen language
or something. I did make some headway a long way back, but I've forgotten
so much of it that I'd have to start from scratch. (Or look at the archive
of the mailing lists perhaps).
So your suggestion is not bad in itself.
best regards,
Christian