The Community Edition was developed by JHNP727. The integration of this into the aLobby is currently in progress (as of April 2021).
If the game is hosted with the classic Gold edition, you can join with both a Classic client and a Community Edition client. However, when the game is hosted with the Community Edition, you can only join if you have the Community Edition yourself.
It will be included in the next aLobby beta version. But be careful: it is a proverbial beta and may therefore contain bugs. We recommend installing a stable aLobby version in parallel so that you can continue to play.
After installing the beta version, you have to select the version you want in the aLobby settings and then restart aLobby.
Translations in the game can be stored as PO files. Details: https://www.siedler3.net/new-version-translations-needed-t10425.html