Keyword significance.

In Google Webmaster reports that both 'post' and 'thread' rates in my top 5 for kw significance.

How do I reduce this?

Google Sitemap Keyword Relevance

Because my forum is another language i made them abit more useful on the custom translation. They look more natural. It's more problematic in other languages. And i cleaned unnecessary words where possible on my theme. (some alt= title tags, explanations, some buttons from guests etc) As much as you remove unrelated words and content, the real content gets more frontier. And you get more targetted traffic. Yes of cource there is an optimum level you can remove things. You should not touch basic functionaltiy of the forum.

For english forums i dont think you should touch the theme, because google has special bots for forums, they know pretty well how to index standart forums. So if you over optimize or change too much the forum. you maynot be crawled like standart forums. The best thing you can do for a forum is vbseo+ good content and more backlinks.