I'd always assumed that the vast majority of spamming/shitposting occurred in the English sections because most signature campaigns only pay for posts in English--and I don't visit any of the local boards so I'd have no way of knowing about any spam problems there.
Many campaigns allow and even encourage posts on local boards, but they also require a report with the translation of these comments into English. Therefore, a huge number of bounty hunters are spamming in these branches. At the same time moderation usually isn`t so responsible and tough there, so spam has every reason for extension. In addition, there is a widespread opinion that the English branches have stricter rules and requirements, whereas in local boards everything isn`t so severe. In the English branches the "elite" of the forum is concentrated, which keeps order (in addition to the main moderators). Therefore, participants apply much more efforts to write quality posts, whereas in local branches comments are usually written for quantity.