Compared to most languages - English is very easy to learn and very flexible - in almost any country today - most of the "elite" and the business comunity can speak English already.
A language almost as old as Aramaic is Welsh - yet this has not stood up well to the inevitable logic of one common language being more efficient - though it is still taking a long time to die - no one could deny that Welsh is a dying language.
One reason for the survival of a language would be that there were ideas that simply could not be expressed in other lanuages (so Einsteins work written in German might not translate into other languages). However there is no evidence at all for this - most ideas can be expressed in almost any language - so the choice of language is purely pragmatic - and there is no benefit to humanity for the survival of any particular language
English is torture to learn for anyone who has an orderly language.
Your understanding of language is shallow. The fact that there are Hebrew words in the Old Testament that set linguists wrangling for years over how to render into English is sufficient to show you wrong. But even in more modern languages there are problems. There are things I could say in Spanish in two words that would take me ten in English; there are concepts in Spanish words that it takes half an hour to explain in English. The same is likely true of any two language pairs I pick.
Only if language is regarded in a very simplistic way, almost as a sey of substitution codes, can it be maintained that there is no evidence that there are ideas that can't be expressed in other languages. Here's a current favorite example of mine: the ancient near east had a literary form known as the "royal chronicle". Its contents could be taken literally so long as they were looked at in terms of the main point, but taken by themselves could not be. It was historical -- but not in any way we conceive of. It had aspects I can only find words for when I'm looking at the pages of some work trying to explain it. I've put a couple of dozen hours into studying this, yet I still don't really grasp what those words, "royal chronicle", mean.
Another example is the word "tomorrow". Commonly, people say that "manana" in Spanish 'means' "tomorrow". But that's a cheap, shallow definition, and in fact a full definition can only really come when you immerse yourself in the language and use it from day to day, and at some point your mind clicks and you get it... but you can't explain it in English without a couple of hundred words, and then the person will stare and shrug.
The adage is "it loses something in the translation." That's true for almost any word that's translated, but it's also true the other way: it gains something in the translation. When reading Xenophon's Anabasis in English, I could see it lost a great deal in translation, but it also gained -- and both are matters of having very few words in one language match their supposed counterparts in another.
Reading the New Testament in Spanish and in English and in Greek sheds light on this. There are Greek words that have to be translated by different English words in different contexts, and by different Spanish words in different contexts. But while in a certain set of contexts two different English words are required, those same two might be served by one Spanish word. Now that could be because the Spanish word has a richer range of meaning, or it could be that the Spanish is so poor that it just doesn't have a word for the other meaning, so one used in a different context just has to do.
Nor is it just words: meaning in many languages is carried in word order, and beyond that in placement, bracketing, and other ways of speaking. For example, if in Greek I have a sentence with the words A, F, C, D, E, F, and G in it, it could be written A B C D E F G or F E D G C B A, OR D B C E F G A, OR B C D A E F G, and each has a different emphasis or meaning.
I like Greek for a reason I hate English -- Koine Greek and Classical even more than modern: Greek has nominative, genitive, ablative, dative, locative, accusative, and vocative cases for nouns and pronouns. It is much more precise! A simple example is the English word "of" -- it can mean "belonging to", or "made of", or "comes from"; in classical Greek there is no such vagueness.
Anyway... each language is not just a set of words, but a worldview. The way we see the world is contained first in our language, because when we use an existing language we stuff the world into its concepts rather than fitting our concepts to the world. There are languages where children don't have to learn arithmetic, because arithmetic is built into the language, languages where there are no "could be" events, languages where all sorts of odd things go on, and each one shapes the way the speaker/user thinks.
So to lose any language is to lose a great treasure.
A multi-lingual world is better. Different languages do things differently.
