Frederico,
I think it's a rather bold conjecture that "The quest for giving a precise meaning to our fundamental concepts cannot be accomplished using natural language" ... without giving an example of a mathematical statement that cannot in principle be translated to natural language.
So I'm in the uncomfortable position of agreeing with your conclusions while disagreeing with the way that you got there. It is surprising to me that you venture into meta-mathematics in your commentary without mentioning Chaitin's leading-edge research (particularly since he is a Brazilian Professor). For example, Chaitin's Omega gives a clear example of an algorithmic compression of a number that is uncompressible (the halting probability of a Turing machine). This example would seem to stand your conjecture on its head: an example of a meta-mathematical result whose natural language translation is straightforward: The number is algorithmically compressible IFF the halting probability of a universal Turing machine asymptotically approaches zero, regardless of the machine language by which such probability is calculated. With this extreme example, I am doubtful that your conjecture is true.
Chaitin has extended his meta-mathematical program to life itself, with the recent publication of *Proving Darwin: Making Biology Mathematical.*
Nevertheless, as a separate subject, I have to agree that what you call a closed theory (and which I would characterize as a closed logical judgment of a mathematically complete theory) is sine qua non -- not only to a final theory -- but to any scientific theory. Closed logical judgements, such as those in relativity, correspond to physical results that make the theory mathematically complete. I like your discussion of quantum theory interpretation, because it clearly exposes why anti-systematic analyses cannot impose a logically objective meaning. Quantum theory is mathematically incomplete. (I don't understand how you reconcile Wittgenstein's anti-systematic philosophy to your philosophy of science, though I would be interested to know.)
Anyway, thanks for a great read and all best wishes in the contest. If you would like to see an information-theoretic take on the Schrodinger's cat problem, and which explicitly uses the excluded middle, please visit my essay ("The Perfect First Question.")
Tom