Locale "best fit" algorithm

[catamphetamine]

Currently only "lookup" locale algorithm is supported (due to its simplicity).
The spec also mentions "best fit" locale algorithm.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_negotiation
I guess it's something more "creative" than "lookup".
I won't ever do it, but if someone wants they can submit a pull request.