A number of studies have consistently demonstrated that those who have an advanced knowledge of the English language are much more likely to advance their careers. In addition to this, these studies have also demonstrated that a strong command of the English language will lead to higher paying jobs, more social mobility, and a great deal of social success.
No matter what career you choose, whether it is Engineering or History, having a powerful command of the English language will greatly increase your odds of success. Generally, your vocabulary will need to be equal to those who are in the same career field.
However, if you want to make yourself more marketable, you will need to increase your English skills, and make them compatible or better to the other people who work in your field. While you may not realize it, people will judge you by the way you speak.