英语 ⇄ 俄语 +

join in on 强调
一般	присоединиться к (деятельности • A new search for the Loch Ness Monster has been announced for later this year and the organizers of the endeavor are calling on NASA to join in on the hunt. (coasttocoastam.com) ART Vancouver)
非正式的	участвовать (E.g., to join in on the fun Wakeful dormouse)