Multitran, the biggest English-Russian dictionary, now has a new online version www.multitran.com with tens of languages. You can translate words in many directions between many languages. Though not all directions have words so far, you can add words and correct words added by other participants. Esperanto-Russian direction has 53473 words. Other Esperantic directions have few or no words so far but it can change very fast.
Now www.multitran.com has become one of the best multilingual collaborative dictionaries. Glosbe.com is also good but it is more complex for people who add words.

53473 words is in both Esperanto-Russian and Russian-Esperanto directions.
Bidirectional English-Russian dictionary has 6618958 words (it seems they are repeated in different topical groups).