The function choose-unicode-string-hash-function
return a function which is suitable for use as the hash-function argument to make-hash-table. The function hash-function generates a hash value for a string, ignoring case using specified Unicode comparison rules specified by style.
The current implementation only supports one value of style:
Compares each character of the string using the simple case folding rules in Unicode 6.3.0.
LispWorks User Guide and Reference Manual - 13 Feb 2015