The thing about pre/postpositions is, their use is almost entirely idiomatic in modern language, i.e. it doesn't follow from the meaning of individual parts and thus doesn't translate without reconstruction.
In English, afaict, practically all adpositions signify relations in space or time, plus there are ‘of’ and ‘for.’ However, once you begin dealing with even slightly more abstract notions, these semantics break―and you just have to pick a word that you will use, without ties to its meaning. “The paper is on the table” is straightforward, as it uses the original meaning of ‘on,’ but you can't say why it's “We speak in English” and not e.g. ‘under English.’
So, German and other languages simply picked different words: it's not like you can complain that some inherent semantics are violated by that.
It's pretty much the same in e.g. Russian with prefixes, since many of them also originally denote spatial relations, and this derivation with prefixes is used in much the same way as with adpositions in English. (Speaking ‘in English’ is actually something like ‘along-English’ in Russian.)
But, English also has a habit of forming piles of new idiomatic phrases, with completely different meaning, by adding postpositions, in the same entirely arbitrary way―which makes learning these phrases an ordeal.