When I install a test version of the Danish language package for phpBB 3.0 Beta 2 on Beta 2, I get in this drop down menu the letters A - Z and "Other". Have checked all files for missing translation of that word somewhere, so I suppose this drop down menu is hardcoded, which it should not be, i.e. in Danish language we have the vocals æ, ø and å, and some common names starting with Ø and Å, not many starting with Æ. Suppose it should be configurable for i.e. Greek without having done a letter analysis for languages with special characters (Greek, Russian etc.), so I also don't know if it it possible to solve at all.
Linked ticket with changeset: r6537