Is there a standard in BIP39?
An ideal wordlist has the following characteristics:
a) smart selection of words
- the wordlist is created in such a way that it's enough to type the first four
letters to unambiguously identify the word
b) similar words avoided
- word pairs like "build" and "built", "woman" and "women", or "quick" and "quickly"
not only make remembering the sentence difficult but are also more error
prone and more difficult to guess
c) sorted wordlists
- the wordlist is sorted which allows for more efficient lookup of the code words
(i.e. implementations can use binary search instead of linear search)
- this also allows trie (a prefix tree) to be used, e.g. for better compression
The wordlist can contain native characters, but they must
be encoded in UTF-8 using Normalization Form Compatibility
I don't think there's any conformance test specified in BIP39 itself. Since Bitcoin is (arguably) decentralised as much as reasonably possible, there isn't really any single person or body who can authoritatively or officially approve lists or tests.
In a List of BIP39 wordlists there are additional criteria that have been applied for some languages other than English.
I believe you could, with careful preparation, engage in discussion with the Bitcoin development community in their preferred fora and subsequently attempt to craft a BIP that is likely to get broad support among both developers and the broader community and submit your BIP to supersede BIP39. You'd have to be sure that others with lower expectations would be willing to go along with the disruption or make careful provision for compatibility with BIP39 and programs that use it.