+HOW TO CHANGE DUCET (NOT WARRANTED)
+
+ 0. rewriting UCA_Version and Base_Unicode_Version in Collate.pm
+ and t/version.t is preferred.
+ 1. replace Collate/allkeys.txt with a new DUCET.
+ 2. run mklocale to generate new Locale/*.pl and Korean.pm.
+ 3. replace Collate/Locale/*.pl with the new Locale/*.pl,
+ and Collate/CJK/Korean.pm with the new Korean.pm.
+ 4. make test.
+ IF FAIL, it may require more changes, not be easy.
+