The correct answer is: communicate.
A universal language would make it easier for people to communicate with each other, regardless of their native language. This would be beneficial for tourists and businessmen who travel to other countries, as they would be able to communicate with the locals and get around more easily. It would also be beneficial for people who work in international businesses, as they would be able to communicate with their colleagues and clients from other countries more effectively.
The other options are not as relevant to the question. Transact means to carry out a business deal, deal means to handle or manage something, and exchange means to give or receive something in return. While these things could be done more easily with a universal language, they are not the main benefit of having such a language. The main benefit is that it would make it easier for people to communicate with each other.