I found a temporary fix for the language issue [] (xx= fr,it,de etc. ) (example= the name of the custom map).


Go to the steam "workshop" folder, then find the folder called "content". After, choose the folder "311210", and finally choose the folder of the custom map which one you get the error message.
The path: ( C:\Program Files (x86)\Steam\steamapps\workshop\content\311210\[Number of the custom map])


Now, you have to rename these two files by replacing -en- by the language selected for your game :
1: en_zm_example.ff
2: en_zm_example.xpak

Example for french language:
1: fr_zm_example.ff
2: fr_zm_example.xpak

it = italy ; de = germany etc.

If you get this error message, it's because the modder doesn't add the languages supports on his map.

Enjoy !