There is: ISO 14651. This is an ISO Standard specifying an algorithm that can be used when comparing two strings. The standard also specifies a datafile specifying the comparison order, the Common Tailorable Template, CTT.
There is the European Ordering Rules. This is an implementation of the iso CTT. It defines an ordering for strings written in languages that are written with the Latin, Greek and Cyrillic alphabets.
There is the Unicode Collation Algorithm. The Unicode collation algorithm (UCA) is an algorithm defined in Unicode Technical Report #10, which defines a customizable method to compare two strings.