Not to contradict the other three responses that I've seen thus far, but yes, since the time you posted tgis question I have been able to access those forums and to post to them. I registered using FireFox for Android and found the captcha code to be a mess of special characters with what I rightly guessed to be the code that would unlock the kingdom buried in the middle of it. There was no captcha image but only that string of gibberish.
It's interesting that there are both an official set of forums through Libreoffice.org and a self acknowledged unofficial set of forums through LibreIfficeForum.org.
That said, I'm not a fan of forums in general, prefering rather the interaction of a mailing list such as this so I'm unlikely to those forums. IMO a forum is useful for archiving helpful hints and the like but I prefer to see active discussions pass through my eMail INBOX. I suppose that if there were only a single FOSS product in which I was interested then I might view a forum differently but I have never gotten into the browser bookmarking mentality. I also have not joined the social media bandwagon so I guess I'm some sort of a Luddite (sp?). Maybe it's a generational thing.