Among the apparently most objective methods of gauging the health of a language is ranking it in order of Wikipedia articles. In June 2009 a whopping 22% of all articles were in English, with 56% in other Indo-European languages (although the language family in question includes Hindi/Urdu and most other Indian languages, in practice the overwhelming majority of the articles are in European tongues). Indeed, the only non-European language in the top ten was Chinese, and that only by user count as opposed to the number of articles.
There are also versions of Wikipedia available in minority languages (Cheyenne, Manx and Maori), dialectalised varieties (Alemannic, Piedmontese and Low Saxon), and creoles (Haitian and Papiamento), as well as dead languages such as Latin (a living tongue only in Vatican City, where celibacy may render intergenerational transmission somewhat difficult), Old English, Gothic, and Old Church Slavonic (currently in use only as a liturgical language).
Irish has just under 30,000 articles (96 in the rankings), Scottish Gaelic just over 8,000 (111), and Scots just under 7,000 (117). Sensibly, there is no Ulster Scots; a proposal for a Wikipedia Valencià was rejected earlier this year on the basis that Valencian is a dialect of Catalan.
One of the more bizarre aspects to Wikipedia over recent years has been the massive number of articles (almost 120,000 of them) in Volapük, the first modern constructed auxiliary language. Indeed, by article, Volapük is more popular than Hindi, Thai, Greek or Tagalog.
Volapük was invented in 1879-80 by Johann Martin Schleyer, a Catholic priest from what is now Baden-Württemberg in south-west Germany. Very popular in its heyday, it was soon displaced by Zamenhof's Esperanto, which was much easier to learn and use. Indeed, at the third Volapük convention held in Paris in 1889, even the tongue's inventor had trouble speaking it, mainly owing to its bewildering array of agglutinative affixes.
When enthusiasts complained about this, and other quirks such as the tongue's complex, German-based case system and the disconcerting effect of excising the letter r
While its successor has itself been subject to criticism, albeit considerably less damning — and arguably better systems such as Ido (an offshoot originally named Esperantido) and in particular Interlingua exist — Esperanto's reasonable functionality and critical mass of supporters have meant that it has not been displaced in the same manner. However, its imperfections, and the rival systems thereby engendered, have almost certainly placed a cap on its development. This is of course similar to the case of traditional Scots vs. "Ullans" or "New Ulster Scots"; any linguistic advantage likely to be gained through even sensitive separate development is dwarfed by the loss of utility.
As for Volapük, as a 2007 debate over closing the Wikipedia portal, which has only one contributor, shows, most of its articles are in fact "bot-generated", i.e. the product of machine translation from other Wikipedias. In the event, it was decided to keep it open, a victory for the wilfully obscure eccentric behind it but also for linguistic diversity in general. As such, we can be grateful.