"여자가 한국어를 공부합니다."
Translation:The woman studies Korean.
Well there are a couple problems with your sentence, which are likely why it was marked wrong.
Firstly, "women" is plural, and "woman" is singular. English uses different verb forms for singular and plural nouns, for example "the woman is" versus "the women are".
Secondly, the Korean sentence is in the simple present tense, and your translation is in the present continuous. The distinction has to do with the completeness of the action; "the woman learns Korean" implies that this action is performed and finished, while "the woman is learning Korean" implies that the learning goes on without ending.
Without the plural marker the word could be singular or plural, so that is not a problem.
Simple present tense is also not finished, but Korean has a present continuous form for things that are happening and you cannot put present continuous for this sentence.
Learn is not the same as study in English and Korean also has two separate verbs.
Ah, I am sorry. Well then. the corrected version is “The women study Korean.” or “The woman studies Korean.” I only answered yours because you said “learns” “implies that this action is performed and finished”. The simple present is not the past. “Learns” can be used if someone learns Korean from a teacher on a regular basis. “Studies” is the work someone does to remember after the teacher has explained something about the language.