How can I say I am very out of practice or "rusty" on a skill?

Question

Suppose I wanted to say

I can speak Korean, but I am very [out of practice/rusty]

Literally translated, this would be

저는 한국어를 할 수 있지만 매우 [연습이 부적해요/녹슬어요]

However, these feel a bit too literal and I am not sure the idiomatic meaning translates well.

Answer 1

You could say 예전에 비해 한국어 실력이 녹슬었다 if you want to imply that it was good before but has worsened over time.

I would rather say:

저는 한국어를 할 수 있지만 아직 좀 더 연습해야 합니다.

or

저는 한국어를 할 수 있지만 잘 하지는 못 합니다.

or

저는 한국어를 할 수 있지만 아직 실력이 부족합니다.

or just

저는 한국어 초보입니다.

저는 한국어를 조금밖에 못 합니다.

Answer 2

If you would like to use the translations with your intension, you can use as follows:

한국어를 할 수 있지만 연습이 많이 부족해요.
(literally, (I) can speak Korean, but (I) lack practice a lot.)

The adverb "매우" is basically rather formal. Furthermore, the subjects are often omitted in Korean, so you can be confused in translating English into Korean. (This is also to me, when I translate Korean into English.)

한국어를 할 수 있지만 많이 녹슬었어요.
(literally, (I) can speak Korean, but (my ability) has been rusty a lot.)

In the second subsentence, the omitted subject is "제 실력." You have to use present perfect.