Why become proficient in speaking English?
It is simple, to be able to communicate in complex English interactions. Being good in what you do is not enough, you need to be able to communicate what you know properly, so the other person receives it, and understands it well.The first from Canada, with really good English and the second one from Georgia (the country). The first student was average in programming, while the second one was superb, very efficient and with an extensive experience and works to show for it.
Whom do you think got a better job after they finished schooling?
The first got a starting salary of $87,000 while the second got a starting salary of $55,000 (even this was hard to find).
Be good doing what you do, and communicate it in such a way that others understand you well. Become an expert in what you do, and English for it pays off.