One easy fix that can be done, is to make your stimuli into an image file (make sure the colour surrounding the stimuli is the same as the background of the experiment) then have the excel file reference the path to the stimuli images, instead of the letters themselves.
There is a few other threads that have discussed using non-typical characters:
https://discourse.psychopy.org/t/text-responses-in-python-input-function-and-dialogue-boxes/12849/3
https://discourse.psychopy.org/t/using-different-languages/17598
Maybe one of these other threads may have some useful information?
Issac