We frequently use definite articles with plurals. It simply identifies a bounded or known set. * I understand all languages. -- unbounded set, applies to every

We frequently use definite articles with plurals. It simply identifies a bounded or known set. * I understand all languages. -- unbounded set, applies to every language, everywhere * I understand all the languages. -- bounded set, applies to a known set of languages, i.e. specifically those languages which are supported by a particular program To be fair, I think "all cases" in this situation is also acceptable.