Good news: the latest Forum trunk resolves the Sticky Threads and Read-only issues. Thanks to the programmers!
Bad news: I still have no found a solution for passing the locale to ForumMemberProfile/edit or ForumMemberProfile/show without adding ?locale=xx_XX in templates, and there are a bunch of items which need it. I think that the key is getting ForumMemberProfile to be aware of its ForumHolder (and so of its locale), but for the moment being all my tries were unsuccessful. There are several DataObject::get_one("ForumHolder") calls that are clearly not getting the correct Holder for non-default locales. Please help!