I installed em client on my Mac. It has installed in Italian (it decided to install it in italian!) I want it in English. As you can see in the image I have no other languages installed and there is no option to install new languages …
If it’s a new installation maybe try un-installing em client, re-download and re-install. When I installed em client (on Windows) it installed with a huge list of languages. I don’t see this list of languages in your screenshot so something may be missing or it didn’t fully install. Try a fresh download of em client (or however it’s done on a Mac).