Hello,

Functional English is a better choice for certified course dear. If you wants to good your communication and writing skills on english then you go for definitely this course. Some University offer this course. IGNOU means Indira Gandhi National Open University offer this couse also for 6 months. After giving the final examination you can get your certificate.

You can do it with your master's degree. But make sure that your master's degree is regular mode and from different University. And your certified course from IGNOU and distance mode. Then you continue your both degree in same time.

All the best.