I also see a lot of spam and discussions that, in my opinion, don't belong on Bitcointalk. Also I see a lot of bounty hunters over there, posting things you can't take serious.
I barely visit the Dutch board, but I assume you mean the Dutch bounty/altcoin boards, right? Those have heavy spam all over the forum, not just in Dutch.
It is just the same with my local board. People are taking advantage of the language barrier in order to spam the forum. The function "report to moderators" is usually used to report posts mostly in english language. Psychologically, it is understandable because you will prefer not to report someone who has the same nationality with you, right?
Can we do something about this and introduce a Merit system for local boards only?
The Merit system works on all boards, what do you mean by introducing it for local boards?
I think he/she is encouraging to increase the merit distribution in the local boards. By increasing the merit regulation and distribution in local boards, we can increase the quality posts and decrease the spam. How about encourage members to apply as merit sources and focus on finding meritable posts on their local boards?