I think the reason you don’t see that is that there are still very few multi-lingual forums and those that exist will chose whatever works best for them.
What about the solution I posted above?
Any specific features you have in mind?
Why is there no crossover? Because the people in each language community have nothing to say to each other (i.e. they’re talking about different things) or because they don’t understand each other or because they couldn’t be bothered to talk to each other because they have enough interesting conversations within their language community?
- In the first case (different topics), there isn’t really any reason to combine them in a single forum.
- In the second case (language barrier), the translator++ plugin could help.
- In the third case (“couldn’t be bothered”), the question would be whether you want to encourage interaction between through the way you organize the forum or whether you are happy with three more or less separate communities with the occasional interaction and “invisible” flow of information through multi-membership.
If you want to encourage interaction between language communities, you might want to consider not creating the same category in different languages but have everyone use the same category and use the translator plugin. If you don’t want to push people to interact across languages, my proposed solution above seems to be the way to go.
A feature that may indeed be useful for several of these scenarios are translatable categories. It has been requested before.
Another unresolved challenge with multi-lingual forums (or even mono-lingual ones allowing users to change their locale) is the customization of the discobot as described in this topic: What exactly are the effects of "allow user locale" - #33 by tophee