Why here is not immersion? It would be pretty useful to translate from English into Russian
Immersion will definitely become available. Duolingo staff tells us that the focus, though, is on having the course released from Beta first. From the logical progression standpoint, there is little sense in providing Immersion unless the course is stable, and there is a large number of users who actually finished it and are ready to take on a bigger challenge.
Прочёл комментарий, но всё равно не понял - что это за режим? чем он сложнее обычного курса?
Immersion is an additional feature -- it allows you to participate in crowd-sourced translation of various texts. A real-life application of your skills, if you will. It's available for some time for other language pairs, but not for Russian-to-English at the moment. You can see "Immersion" it in the top-level navigation bar if you enroll into some other course -- English-to-Spanish, for example.