It is generally assumed to be axiomatic that all languages have the same descriptive power. It is more that there is no good counterevidence to this, than that there is any obvious proof.
One important point is the infinity of languages: that we can generate longer and longer sentences, from a finite, relatively small, set of words, and build up sentences of any imaginable length, and therefore can express many ideas, although certain ideas may take longer to express (and may be longer in some languages than others). There has been some research into questions like the information rate (over time, e.g., per second) of different languages, but it's not entirely clear what the point of that research is, or what the results should mean, and it is controversial how to measure it anyway. In short, there are probably better questions to ask.
