1. 내 한국어를 높이고 싶어. 높이다(vt) = raise; lift. 2. 내 한국어를 늘리고 싶어. 늘리다(vt) = increase; augment. 3. 내 한국어를 향상시키고 싶어. 향상시키다(vt) = improve; enhance. 4. 내 한국어를 나아지고 싶어. 나아지다(vi) = improve; get better. In Korean, we talk about 한국어 실력(Korean skills) much more often than just 한국어 in this context. 높이다 doesn't collocate well with language skills or knowledge that well. 늘리다 can be used with knowledge and skills, albeit not the best choice. 향상시키다 is a good choice but sounds too formal for everyday speech. 나아지다 is intransitive, so it can't be used in this context. You can use it like 내 한국어가 많이 나아졌어. You can say it as follows: - 내 한국어 실력을 늘리고 싶어 = I want to augment my Korean skills. - 내 한국어 실력을 끌어올리고 싶어 = I want to lift up my Korean skills. (끌어올리다 = lift; pull up) - 내 한국어 실력을 향상시키고 싶어 = I want to improve my Korean.

고마워요

2nd and 3rd are good ones, but 4th are worst. and 1st is somewhat awkward.