It's been happening to me for quite some time, I can't tell if it was always there or if it was introduced at some point, yesterday I happened to disable the tag-related extensions for another problem and finally realised that Payments was causing it.
Basically enabling Payments hides the FoF Discussion Language dropdown in discussions, I've tried to test if maybe one extension should be enabled before the other, but it doesn't seem to change anything.
*This is the dropdown that disappears