Still a lot of work to do, still (almost) no time to write. Let’s break the radio silence with the simplest kind of post:
a collection of links. This time it’s the best language forums I found:
Zompist Bulletin Board – frequented mainly by conlangers (people who design languages for fun and – sometimes – promise of profit), lot of interesting information to get from there. Most users have native or native-like coimmand of English, so the discussions are less childishly polite than on some other places.
Unilang – probably the biggest one around. Has many sub-forums devoted to particular languages but their quality varies wildly (but the Persian one is simply excellent thanks to the tireless and always helpful alijsh). In my experience, the main forum (for all languages) is a waste of time consisting mostly of teenage chit-chat.
Lingvoforum – the biggest Russian forum I found. Top quality, with lots of links and no shortage of people both knowing what they are talking about and being able to express themselves very well.
Amalgrad – tightly moderated Russian forum focusing on Middle Eastern languages. Invaluable treasure trove of resources, but nothing will save you if you break their rules.
Forum.jzn.pl – a husk of a Polish-language forum which never gathered enough momentum to kick start. Back in the day I was one of the most active posters there. UPDATE: an attempt to revive it is underway.
These are what I found to be the best, but undoubtedly your judgement will differ from mine. Do send me your opinions and suggestions. I would be really grateful for links to language forums operating in languages other than English, Russian and Polish.