the language will be useful when you ...приедешь в Россия, потому что в России мало людей хорошо знают английский
without knowing russian it will be difficult to ...купить продукты или билет на метро.
Язык будет полезен когда ты ...
Без знания русского будет тяжело....
The language will be useful when you come to Russia, as so few people speak good English here.
Without knowing russian it will be difficult to buy groceries or a metro ticket.
Если правильно понял вопрос, то:
The language will be useful when you ...go to Russia because few people speak English well.
Without knowing Russian it will be difficult to ...buy food or a subway ticket.
The language will be useful when you come here because there are few people in Russia who know English well.
Without knowing Russian it will be difficult to buy food or an Underground ticket.
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