fix(admin): switch the language from a menu of the top bar
The language button of the panel opened the dialog of the language module of the site through a copy of its modal script, and the copy posted for the dialog without a token: the panel got 403 and an endless spinner. It also broke with the language module switched off.
The button opens a dropdown of the languages on offer instead, each a link with ?setlng=, which the core reads on any page: no module of the site, no request behind the scenes, no script needed. language-menu.js keeps the rest of the query of the page and takes setlng out of the address afterwards. The copy of modals.js and the empty ajax modal of the admin layouts are removed.
The button opens a dropdown of the languages on offer instead, each a link with ?setlng=, which the core reads on any page: no module of the site, no request behind the scenes, no script needed. language-menu.js keeps the rest of the query of the page and takes setlng out of the address afterwards. The copy of modals.js and the empty ajax modal of the admin layouts are removed.