And what gets lost between them?
If you read a translated book or subtitles you're not reading what the author wrote, it's the translator's effort. I know enough of a couple of languages to know that quite often what's being fed to you is radically different to the original work.
Similarly if you're some guy from Lesotho who only speaks your local dialect, how much of the world's knowledge is being denied to you by the lack of translation? What about your government as they're likely to be the one and only news source in that language? Surely objectivity and neutrality is almost non existent if someone's information sources are that limited. How much of his knowledge is being denied to anyone who doesn't speak what he does?
There must be mountains of information, art and learning that disappears between cultures because of this.
Is this an unpublicised cultural disaster or does the right info always find a way?
Anything worthy of note and public attention will get translated to English eventually or is just written in plain English first. So there's no reason to think that mountains of information get lost.
What do you consider as worthy of note and public attention? You can have a different definition of that.
Translate a document has a cost, either, the document or whatever needs to have a value and so it will be translated. Either it has no monetary value , in this case, it can be translated by a researcher, or more likely, won't be translated at all