Well, thank u very much to everybody!
I agree with you all: he could have learnt it. Since what i'm writing takes place AFTER the murder of the imperial family, it's far more easy to think he actually speak russia - at least a little. I tought he spoke in french, for example, with Gilliard; but i think it's quite impossible not to learn a word of a language, in which country you live for a long time.
Moreover, i was thinking about the fact, that Gilliard and Gibbes stayed in Russia for a while after the if's murder, collaborating with the White Army; we all know in the army there's not only learned people; it's possibile that most of them knew French... but english? Only aristocrats, In imperial russia, knew english, as i know; so, i think he spoke a little russian, just to make himself understood...