Even though the English language is probably the most popular language in the world, still every sixth person in the world speaks Chinese for example. There are simply many languages in the world that will not cease to exist even though English is so popular now and it seems that so many people use it to communicate.
When I was back in secondary school, I remember learning that there are about 6000 documented and undocumented languages in the world. The number does not cover dialects or any other variations of a language. You have to admit that the number 6000 is pretty impressive. There is no way one person can know all the languages in the world. It usually takes a lifetime for a person to even master one or two languages not to mention three of them at once.
I predict that the future of translation agencies is indeed bright. Nothing indicates that the number of languages in the world is going to dwindle any time soon. On the contrary, even though the English language is so popular these days and it seems that many people choose to learn it and speak it, the demand for translation agencies is indeed on the rise. Just look at some numbers and you will see that so many people these days opt for translation services that it would be foolish not to give them what they want.