The web server as configured attempts to negotiate with the viewer's browser to select the appropriate language. This means that participants who have configured their browser to (e.g.) prefer French will get a French version of each page if it is available.
This did cause some problems as city coordinators who customized things did not wish to make customizations in both languages. The result is that for unilingual web sites unedited pages of the opposite language sometimes were displayed.
The enhancement, as detailed in PR#428758, is to make some changes to the way that unilingual web sites are instantiated from templates. This may interact poorly with the desire to easily customize the pages.
There are a number of other minor changes that should be done, for instance creating a new database entry for the French name of each department.