Thinking about this, en.wiki has an interesting structure https://en.wikipedia.org/wiki/Category:Redirects_from_non-English-language_t... Maybe if you could measure the usage of these redirects by language, you could estimate the relative population size of the wiki-using speakers of that language who currently use en.wiki? The measurement might be sharpened by a push to classify https://en.wikipedia.org/wiki/Category:Redirects_from_alternative_languages Presumably other structures exist in other wikis that could be similarly measured.
cheers stuart