Trying to build a mutiple forums in one forum set (Features)
I'm just doing this.
I cheated, and it's not perfect but works really well.
In the name of sharing knowledge:
I had the initial installation in a folder called forum, and then copied that and named it forum-french etc.
I also duplicated the tables in the database called entries and entries_cache and renamed them to entries_french and entries_french_cache.
Then in config --> db_settings.php I updated the 2 values there; and also in includes --> functions.inc.php I changed backup_entries_ to backup_entries_french_ (not tested yet).
So the normal forum is at domain/forum and the french one is at domain/forum-french.
Works like a charm! It does mean that you have 2 main.tpl files; but this can be a good thing.
Hope that helps,