Symptom

wxMaxima halts when Maxima processes Greek characters or Umlauts.

Suspected diagnosis

Your version of Maxima is based on SBCL.

Possible cure

If your Maxima is based on SBCL the following lines have to be added to your .sbclrc:

(setf sb-impl::*default-external-format* :utf-8)

The folder this file has to be placed in is system- and installation-specific. But any SBCL-based Maxima that already has evaluated a cell in the current session will happily tell where it can be found after getting the following command:

:lisp (sb-impl::userinit-pathname)