Hi, I recently wondered myself, why I can’t switch languages in manjaro cinnamon so easily and found out, that cinnamon dropped the language module (for control panel) already in v2.2
Luckily there is mintlocale in the AUR, but I think it’s so essential it should be a dependency for cinnamon.
I have started to use this as manjaro settings manager is difficult to set these days with the changes to the locale.conf file. Using this first allows setting manjaro settings manager with ease. Incidentally until this is done gnome-terminal will not start.
This might not be needed not sure need to do more tests, it seems if /etc/local.conf is being populated with all the locale info and gnome-terminal does not like this.