There is [ISO 14651][1]. 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][2]. 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][3]. The Unicode collation algorithm (UCA) is an algorithm defined in Unicode Technical Report #10, which defines a customizable method to compare two strings.

  [1]: http://en.wikipedia.org/wiki/ISO_14651
  [2]: http://en.wikipedia.org/wiki/European_ordering_rules
  [3]: http://en.wikipedia.org/wiki/Unicode_collation_algorithm