This isn't to demean the rosetta project in any
way; they already have
thousands of languages, and a million dollar grant from the US
government to continue their work. But I think one of Wikipedia's
important side-effects is its
potential to preserve (and store useful, even self-bootstrapping,
content in) disappearing languages.
Well, if the goal is to preserve ancient texts in the language, I could
see wikisource as being a better location. To have a viable Wikipedia,
there needs to be an interest in using it as a living language, one in
which you would write about everyday topics in. I can see this for some
recently-revived languages---people might be interested in there being a
Cornish Wikipedia their children can look up information in. But is
anyone going to look up anything in a Gothic encyclopedia? Will there
be articles on global warming written in Gothic? etc.