Could it be that the Russian language itself is very complex itself, so all the needed brain cells are already used up by it? No!

However, Russian and English are very different, so native speakers of Russian (including myself) usually have the following problems with English:

1. A and the. Russian has neither the indefinite nor the definite article. This means that natives of Russian tend to omit both articles or use one instead of the other.

2. The word order in English sentences is much stricter than that in Russian sentences. So natives of Russian tend to make many mistakes copying the Russian word order.

3. Verbs and tenses. They are a nightmare.

These problems are typical for natives of Russian who are learners of English.