In order to see the coverage of wikidata by language.
The following could be used for user interface language
SELECT count(*) as count, COALESCE(up_value,'en') AS language FROM user LEFT JOIN ( SELECT up_user, up_value FROM user_properties WHERE user_properties.up_property = 'language' ) AS b ON user.user_id = b.up_user GROUP BY language ORDER BY count;
Babel languages may be a better.
These can be counted using numbers of users in categories, for example Category:User_en-N etc.