local_hub plugin accepts only submissions where the language is one accepted by Moodle. Looking at the database, I will risk saying that this dates back to March 6, 2015.

The problem is, a lot of older (or not so old) Moodle versions send locales (es_mx, fr_ca, etc.) to the hub in the language fields. The data I see in the database tells me that these sites have been unable to update their registration since the change was deployed.

A good example of this can be seen by the following query: select name, language, moodleversion, moodlerelease, timemodified, timeregistered, url from mdl_hub_site_directory where deleted = 0 and url like '%decclic.qc.ca';

I know for a fact that all these sites run off the same codebase. But those with "fr_ca" language all stopped updating on the same day...

It looks like this is a change in Moodle's code, somewhere in the language codes provided by the string manager.