And reg tendency to gravitate towards a single langauge:

Depends on what area of life we look at.

Cultural areas like music, news, media, religion, movies, art, literature will always be local languages no matter how much one tries to change it.

Professional, economic and business requirements may require people to learn English, Bengali, Urdu, Hindi, Spanish, Chinese, Japanese, Korean, etc. depending on who the person is economically interacting with.

Legally and politically, yeah. There could be a tendency for one universal language to emerge. English has by far the best chance at getting there because of the advancements and scholarship that has been made using this language.