The problem with smaller sub-forums is the audience. Your post will be only read by less than 1% of the members. So if you need some help or new ideas, it won't lead your very far, unless it is a specific matter such as local gatherings or Dutch tax issues. Would be just a bit of socializing.

Fat Tails, I believe that your argument has validity as the current "audience size" for a Dutch forum appears to be insufficient or limited to justify a sub-forum, but who am I to judge. Conversely, I do believe that a "miscellaneous category" within the other language section could have some utility to all the users, by this I'm referring to those whose language is not included in the sections. If they grow to an substantial amount they could potentially establish their "own language section".

Honestly I'm indifferent about the situation as I might was well use the English forum's but these are just my 2 cents.