Russian language is considered hard for several reasons: 
1. The use of Cyrillic alphabet, which differs substantially from other alphabets. 
2. Russian language contains several unique sounds, which are hard to pronounce for foreigners. For example: [ы] and [э] are considered hardest sounds to learn in Russian. 
3. Grammatical complexity. Russian language has 6 grammatical cases for nouns and adjectives. For example modern English has three but for pronouns only, German has four and Spanish has 5. 
4. Russian language contains a lot of exceptions, which makes it challenging for non-native speakers.
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