We need more requirements. I'd like to submit the following as a starting point:
I'm assuming you mean this post to be modded funny (i.e., ironic)? Otherwise, I think you're overlooking some major problems in how language actually works.
* Must be usable with respect to the correct chronological context. Consider how the first 10 amendments to the US Constitution have been hashed over, in the last 200+ years. We need to be able to reference the exact version of the language, as used, in any legal script. This will keep lawyers from interpreting version 1.0 laws using version 2.0 rules and definitions. Alternatively, the task is monumental: create a language that will stand as valid speech, *forever.*
Exactly how do you define this language other than referencing its own terms? And if you do so, don't you think the lawyers will start arguing over the meanings of the definitions, or the meanings of the definitions of the definitions, or the [insert infinite recursion here].
For a practical historical example of this process, see Jewish law and rabbinical interpretations of the Torah. There's the original text, and then there are commentaries that explain the text, and then there are commentaries that explain the commentaries. And the process is never-ending.
And the problem with the Constitution is NOT that we don't know what what the Founding Fathers meant. Sure, there are some places where there's ambiguity or where we could argue about how a particular 18-century principle would apply to a 21st-century context that couldn't exist in the 18th century. But, with a few exceptions, we actually have a pretty good idea of what the terms used in the Bill of Rights meant at the time. If you object to change, the problem isn't the language -- it's our legal system, which draws its authority not only from written law but from court precedent for interpretation. Some parts of the Constitution simply don't mean what they originally did -- not because we lack understanding of what they originally meant but because legal precedents have gradually shifted the meaning. And overturning those precedents would in some cases essentially require trashing a century or more of jurisprudence and all of the precedents built on top of it.
In sum -- interpretation is always an inexact science. And no matter how exact your laws are, new situations will crop up or social values will change, and interpretations will adapt, no matter how much the language authorities try to crack down on meaning shifts. It's a systemic and social problem, not a purely linguistic one.
* Must be amendable. Amendments to the language must not be permitted to collide with existing definitions. I would go as far as to say that synonyms and homonyms must be strictly prohibited; a side effect here is a relatively pun-free language.
Sounds incredibly boring to me. Anyone who reads fiction (let alone poetry) would find this language completely ridiculous and lacking any useful expression. Real people would likely abandon it immediately or at least come up with their own puns or synonyms or whatever.
* The definition of anything must be readily quantifiable, without ambiguity, right down to the planck constant if need be. Recommending the strict use of SI measurements for both space and time.
Okay, for a start -- please define a basic common word in your "readily quantifiable, without ambiguity" style.
For example, please define "chair." I'll even make it simpler and not insist that you define metaphorical uses -- just come up with a "readily quantifiable, without ambiguity" definition that precisely defines the kind of "chair" that people sit in.
And then after you're done, I'll build something that doesn't fit your definition exactly, and I'll sit it in -- and then I'll sell it as a "chair" to people. Guess what? Your precise language is overridden by popular use... like any real-world language.
* An improved version of these requirements must be penned in version 1.0 of the language, to be followed immediately by version 2.0
Even the French Academy (with its immortels) couldn't stop "Le Big Mac" from joining the French popular language. You really think you could ever nail language down like this??