Trelby is written in Python (using the python bindings for wxWidgets).
Someone made an unofficial packager for dictionalries.. but right now
you can only change the dictionary manually. It would be a welcome
addition if you can add the feature into trelby. Note that the words
in the dictionary are limited to Latin- character set.
You can lookup the relevant issue in the issue tracker for more info,
and link to the unofficial tool.
~Anil