A drop down list box is a common solution to this
exact sort of
problem. It could be sorted so that the most popular languages are
at the top, and the rest in alphabetical order, with "popularity"
determined by either number of articles/contributions or number of
hits or number of native speakers of the language or whatever.
But as Brion has pointed out, it's a bad solution, because it hides
information that varies a lot per page. I personally don't think long
lists are a problem, esp. with a smaller font. We should just adhere to
the simple principle: Only link if there's really a page at that place.
Instead of having the redundant links in the main page body, I think we
should put a text there:
"Wikipedias have been set up in every world language. The ones linked on
top are the currently active ones. See [[Multilingual coordination]] for
information on starting a Wikipedia in your language."
We should, of course, add Wikipedias that are reasonably active (e.g.
Chinese, Russian, maybe Catalan) to the list of interlanguage links on
Main Page.
And if "scalability" really should ever be a problem, we can set a
threshold of language links per page at which a dropdown is used, or the
links are shortened, or whatever.
Regards,
Erik