I couldn't fully understand your question
So i will translate this sentence '내가 한국어를 잘하게 되는 정도 열심히 공부했다' as 'the reason i can speak korean well is that i studied hard.'
If i change this into korean, it will be '나는 열심히 공부를 하여 한국어를 잘 하게 되었다.'
Have a good day!