hasn’t it been suggested that the internals of google translate and similar systems have effectively constructed such a meta-language?

It seems like you could construct a meta-linguistic sentence by writing a phrase in one language and choosing from possible translations in additional languages, which would hone the cross-linguistic meaning. You might not even have to define a representation of the metalanguage, you could just keep a set of (phrase, score) tuples, and interpolate translations of those phrases into the target language at display time! that almost sounds practical to me