Here is a list of language-regulating bodies. There is none for English, but they exist for Spanish (Real Academia Española), French (Académie française) and Swahil (Baraza la Kiswahili la Taifa for Tanzania, Chama cha Kiswahili cha Taifa for Kenya).
No language regulator addresses the issues which arise in the interaction between natural language and the needs of legal interpretation. Instead, these bodies generally strive to maintain the historical "purity" of the language. Rather than "define" a word like "sandwich", they decide whether to outlaw (or disparage) the word because it comes from English.
The vast majority of language-related problems in law which arise in common-law countries pertains to characteristics of common law and the practice of establishing precedent. There are philosophical conflicts, for example between those to adhere to the text versus those who try to discern original intent. If we had an official agency that precisely defined what a "weapon" is, we would still have the struggle over interpretive philosophies which renders moot any rulings from the national language regulator.
In the US, part of the problem of word-definition is the widespread practice of localized redefinition in statutes – the laws that say "In this subsection, 'weapon' has the meaning defined in 18 U.S. Code §920" (fictitious: §921 defines "firearm" undefined "weapon"). Tracking the scope of definition and range of variation of a word within a body of codified law is very difficult.
The rule in common law is that words that are not statutorily defined are given their "ordinary" meaning. There is no authoritative resource for "ordinary meaning" in English (there is no such thing as "the" dictionary). In the US, it would require a constitutional amendment to immutably impose a particular dictionary standard for deriving word meaning (e.g. Webster's Fourth New International Dictionary of the English Language, Unabridged, forthcoming) and there would be ensuing political protests. A legally precise definition of "repair" would be very difficult to understand, and would require hiring a lawyer in order to engage in the activity of "repairing broken windows", from a legally-safe perspective.
And that is just word meaning. Ambiguity in sentence-meaning cannot be resolved by listing the sentences.