This faq is on using the forum search feature to filter posts by language.

Top of each page right hand side is the "Advanced Search" link, click it.
Then click "Single Content Type". Then select "Forums" in the drop down.
Select "Last Visit" in the date drop down, then select "Save Search Preference".

Then you are all set. Thanks goes to shamanvirtuel for pointing this out.

Also as per the announcements the new languages that are available can be changed, in the lower left hand drop down of each page.