A DESCRIPTION OF THE PROBLEM :
some thoughts after watching JDK-8285001: Simplify StringLatin1.regionMatches

            if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
                continue;
            }

should be changed to

            if (((u1 == c1) ? CharacterDataLatin1.instance.toLowerCase(c1) : c1) == Character.toLowerCase(u2)) {
                continue;
            }

as:

1. c1 is LATIN1, so CharacterDataLatin1.instance.toLowerCase seems faster.
2. because c1 is LATIN1, so if u1 != c1, then c1 is already lowercase, and don't need a lowercase cauculation.