Translated fragment of the forum rules:

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4. The main forum language is Russian. Posts written in other languages can be deleted or moderated. Use online translators. If you can't find any - here is the normal one.
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Only form of the application for entering the clan is translated.

Also all conversations in clan/ally chats are made in Russian. So if you want to participate you'd know some common Russian words and phrases.
If your apllication for entering the clan will be accepted, i'll make some important commands (during Sieges, Raids) in English in ally chat for the first time, but later i won't do it, because it is difficult, to analize sitiuation, communicate with other leaders, make decisions and commands and translate them at the same time. If you are ready for starting learning Russian, write an application if you want, if not - don't waste your time.