I built the pages on my system and the navbar contents for index.eo.html (main page) are translated. So I don't know what else I can try.
It is most probably something similar to a problem I had a few months ago (cf. the discussion starting from http://lists.debian.org/debian-www/2005/11/msg00120.html). The relevant bugreport is #338484 (http://bugs.debian.org/338484). The locale file provided by Frank Lichtenheld has the eo_EO locale commented (maybe this locale is not supported by the Sarge glibc?), so this locale is probably not built on www-master and this would explain the problem you see here.
That is *exactly* what's happening. And that's why it built ok in my system. Thanks a lot! I'll see if I can reopen the bug or file a new one, attaching the locale. Eduardo.