No, but what I’ve discovered is:
– if I do WordPress reinstall (trough the dashboard/updates) then the language appears
– if I don’t do anything for 24 hours, language files appear in some magical way. I say magical, because it is not in the listed WP’s cron jobs (I’ve tried to manually run all of them to see which of them eventually download the language).
So generally this is WordPress problem/bug, who knows. You can try yourself the described scenario to see it live (1. WordPress + theme installed 2. change the language to some different than the default English).
So with simple words:
a) if the language is changed BEFORE the theme is installed, after the theme installation, the language is OK (downloaded immediately)
b) if the language is changed AFTER the theme is installed, after the installation there is no language files. They appear later somehow, or after WordPress core reinstall.