The Ethnologue, the most widely used catalogue of the world's languages, has instituted a restriction on how much content is available for free on their site. After 7 data pages per month (excluding "navigation pages, indexes, and other "administrative" pages that you may need to access to get to the data you want to see") you will need to be a subscriber in order to access more. The cost is 9.95 USD per month, or 60 USD per year.
This is quite simply due to lack of funding (cf Linguist Lists funding drives), you can read more about this in their official blog.
Which then are the most useful 7 pages? I would say the ones found under "statistics", check them out!
Already before this there was certain content that had to be purchased ("country reports" for example)
and a physical version. There are also rumours that the glossaries of linguistic terms (the monolingual English one and the bilingual French-English one) might be restricted in some way, so that the paper versions will sell more. However, those are only rumours <insert non-first hand knowledge evidentiality marker>.
Image from the 16th edition of the Ethnologue, each dot is one language. © 2009 SIL International
There's more posts on this blog about Ethnologue (a few quite informative ones), you can explore them here.
I noticed a thread on twitter about this topic after having made this post and just to clarify SIL International maintain both the Ethnologue and the ISO 639-3 standard for language names, this decision on subscription however only affects the Ethnologue website and does not apply to all SIL Internationals resources. You can access information about the ISO-coders here at their official site and you can also search language names and the glottocodes and ISO 639-3 on Glottolog (which often contains more alternative names than Ethnologue anyway). There are other ISO-standards for language, and they are all open, and there are also Glottocodes. Always, always remember that the ISO 639-3 is technically for language naming and that ISO works for proprietary, industrial and commercial standards, they are not necessarily always useful in all research and can and should be critiqued when necessary. The ISO 639-3 is linked in such a way to Ethnologue that is also aligns with SIL Internationals language classification - judgements of what is and what is not a language. For more on standardisation of language classification, go here and also other posts tagged for Glottolog and/or Ethnologue.
There was also a statement in this twitter thread that this pay wall most likely will only effect 5% of Ethnologue's users. I do agree with Simon Greenhill that the 5% who do pass the 7 page limit are most likely doing very interesting stuff (cough cough like yours truly) and there should be another way to fund Ethnologue, much like the DFG funding Open Access enterprises in academic publishing. Also, I'm sceptical that the money generated by these 5% will really be significant in the running of Ethnologue.
As far as I know, Ethnologue doesn't as far as I know get regular academic funding through research councils and the likes for running Ethnologue, but more from churches and bodies involved in the christian mission. Again, I don't know this certainly because I haven't seen their books.