We should not standardize one language as the worldwide primary language. Yes, it can make international communications easier but right now - without such a language - we're managing just fine.
At this point in time the world has more than enough problems and teaching everybody one language - without there being an actual need for it - is a waste of resources. It's much more important to focus on creating piece, enable everybody to get a proper education etc. than it is to 'force' everybody to teach a language they don't need.
We should standardize one language as the worldwide primary language because if there are many different languages, it will prove to be a major barrier. For example, say you work at a hospital. You receive a patient who appears to have had a heart attack. You try to ask her if she has a history of heart problems or is in pain. There's only one issue; she doesn't speak English. Now you have to search for someone who can translate. This could cause your patient to die. This would not happen if there was one standardized language.
While it is true that it can lead to problems, is it really worth going through all the hassle it would take to teach everybody a new language just in case something goes wrong? Besides, things like that can still go wrong: if you have a deaf person who doesn't have a translator then you can still have problems like that even if everybody did speak the same language.
The world has bigger fish to fry than this. If someone chooses to learn a second language because they feel that it would come in handy then fine! Go ahead! But forcing everybody to learn something will just discourage people, nobody likes to be told what to do.
Yes, teaching everyone a sole language would be difficult but it is all worth it in the end. It would mean being able to trade world-wide and boost our economy big-time. Only one generation would have to learn the language. Say the language was Mandarin. About 14.4% of the world speaks Mandarin. If one generation after another learns from the other, we could get that number to 99%. Of, course deaf people would have to learn Modern Chinese Sign Language.