The word "учить" means 1) to teach and 2) to study/to learn, but it depends on its grammar government: 1) something (dative case) - Она учит русскому языку. = Она преподаёт русский язык. She teaches Russian. 2) something (accusative case) - Она учит русский язык. She is learning Russian.

X가 언어를 곰부 해요. Она учит русский язык . There is a feeling of 받다 (receive something) and that is the reason why Accusative case is used - because it answers the accusing questions: accuse who or what? ) Она/он учит Русскому языку - you can translate as X가 언어를 곰부 하게 해요. (feeling of giving something TO someone or forcing someone to do some that is why the case is called DATIVE (from word "дать - give" кому, чему? to whom? to what? ). I think this is why Russians students who just begin learning English translate this sentence in English as "She is teaching to Russian language. " because in Russian you simply don't" teach something", instead you "teach to something".

The verbs учить-выучить are usually used in the sense of learning a skill, or in studying elementary courses. These verbs cannot be used without a direct object.

The verb pair учить-научить is used to indicate that someone is teaching someone else to do something. The person taught will be in the accusative. The subject taught will be in the dative case. Наташа учит студентов русскому языку. Natasha is teaching the students Russian.

to teach = учить, обучать. to study = учиться, изучать, обучаться.