russo

In a sentence

• 我有一个俄罗斯朋友，他的名字叫亚历山大。

  I have a Russian friend whose name is Alexander.

  In this sentence, '俄罗斯' (Russia) is used as a noun referring to the country. It describes the nationality of the friend.

• 俄罗斯文化非常丰富，我喜欢他们的民间音乐。

  Russian culture is very rich, and I like their folk music.

  Here, '俄罗斯' is used adjectivally as a noun adjunct to specify the type or origin of the culture being referenced.

• 学习俄语有一点困难，但非常有趣。

  Learning Russian is a bit difficult but very interesting.

  Here, '俄语' (Russian language) is derived from '俄罗斯' and specifies the language spoken in Russia.