The adoption of rationalism implies, moreover, that there is a common medium of communication, a common language of reason; it establishes something like a moral obligation towards that language, the obligation to keep up standards of clarity and to use it in such a way that it can retain its function as a vehicle of argument. That is to say, to use it plainly; to use it as an instrument of rational communication, of significant information, rather than as a means of 'self-expression', as the vicious romantic jargon of most of our educationists has it. (It is characteristic of the modern romantic hysteria that it combines Hegelian collectivism concerning 'reason' with an excessive individualism concerning 'emotions': thus the emphasis on language as a means of self-expression instead of a means of communication.) (Karl Popper, The Open Society and its Enemies vol. II: Hegel and Marx, Routledge 1945/2003, p. 264)While this quote is mainly about how you should use a given language, rather than which language to use, it clearly suggests the desirability of some international language, and Sapir's idea of how such a language should be built happens to be rather Popperian in spirit:
It [the international auxiliary language] must, ideally, be as superior to any accepted language as the mathematical method of expressing quantities and relations between quantities is to the more lumbering means of expressing these quantities and relations in verbal form. This is, undoubtedly, an ideal which can never be reached, but ideals are not meant to be reached; they simply indicate the direction of movement. (p. 51)... National languages are all huge systems of vested interests which sullenly resist critical enquiry... (p.60) Intelligent men should not allow themselves to become international language doctrinaires. They should do all they can to keep the problem experimental, welcoming criticism at every point and trusting to the gradual emergence of an international language that is a fit medium for the modern spirit. (p. 64, Edward Sapir, "International Auxiliary Language" in Culture, Language, and Personality, Berkeley: University of California)So it is all the more ironic to find that Popper's paragraph continues with this:
And it implies the recognition that mankind is united by the fact that our different mother tongues, in so far as they are rational, can be translated into one another. It recognizes the unity of human reason.This seems to imply that linguistic diversity is worthless: if something is rational, it can be explained in any language, and if it can't be explained to me in my language, it must be irrational. I rather suspect that the Sapir-Whorf hypothesis was partly intended as a rebuttal to this sort of argument. If your language tends to blind you to the differences in logical form between sentences with superficially identical structures (his example in the very essay quoted above is the perfective/imperfective distinction in English) and makes it easy to spot the differences between ones with different structures, then the ideal auxiliary language should allow you to express logical form as unambiguously as possible; and to be able to make a language free of your own linguistic biases and blind spots, you will have to carefully study many languages of as many different types as possible.
Of course, that begs the question: is there such a thing as an overall better language, or is that whole approach misconceived? Algebraic notation is unquestionably superior to English for describing physical laws, but it's not a very effective way to make a grocery list. In practice, people use different languages, and different technical vocabularies embedded in the same language, for different purposes.