苦练内功 英文怎么写

practise internal work relentlessly

内功internal work

practice your inner ability with effort

No,it depends. Context is needed here.
1. To improve oneself.
2. To train to be more qualified.
3. To promote oneself in one's qualifications.
4. To meet the needs of one's post.
5. To make oneself fit for one's job.
We still have some more expressions, it depends on the occassion.

Trains hard the basic skills