Adding "를" after "한국어" would definitely increase the fluency of the sentence. Besides, that you're good! Also, what Mojave said actually makes the sentence sound very weird. It's almost like saying, "If I had the ability to speak Korean better, it would be great." It's implying that you have no ability to improve at all, when the case is that you DO have the ability. Just "저는 한국어를 잘 할수있으면 좋겠어요" sounds the most natural.

저는 영어를 잘 할 수 있으면 좋겠어요.

thank you Mojave^^

I'm learning Korean, so certainly a native's answer will be better. But... in English, I would say "If I COULD speak Korean better, it would be great." and I think it might translate better to Korean too. That just requires adding -도 to 수. 저는 한국어 잘 할 수도 있으면 좋겠어요.