As I've already mantioned in my last post wpForo doesn't support Multi-language websites, you can't use /en or ?lang=en or other switchers yet. You can only use wpForo on single language websites. The .MO and .PO files of Russian translation is in wpforo/wpf-languages/ folder and those work fine. All language files must have wpforo- prefix like wpforo-ru_RU.mo and wpforo-ru_RU.po. 

We've already asked in Poliglot to add @dobrodukh as wpForo Russian translation Editor here:

https://make.wordpress.org/polyglots/2016/08/14/hello-polyglots-i-am-the-author-of-plugin-4/

This request has been approved and we're waiting for @dobrodukh to manage and approve Russian Translation. But you still can use his translation. It's not depended on Polyglots status. Just change WP language and you'll get wpForo in Russian.