You will need to install a user script manager extension to install this script.
This script allow the use of a default language by editor.
The language is defined on the first use, the default and current language selection is typed by the editor.
after the installation, at the first connection to the WME, you'll be prompted for the language and the current language of the page will be the default.
the selection is the same as needed by the WME, ex: fr for french, nl for nederlands, de for deutch...
Don't hesitate to contact me if you've any questions
Install Tampermonkey/Greasemonkey depending on your browser.
Then use the following links to install.
Click on the language next to your username or go to this url : https://www.waze.com/editor/#reset-WME-prefered-language