Unicode support in Slicer is limited. It is supported at Python and Qt level, so it is possible to display Unicode characters to the users.
See these pages for details:
- Slicer Internationalization
- https://projectweek.na-mic.org/PW30_2019_GranCanaria/Projects/UltrasoundSimulatorTraining/ (see “Background and references” section for source code of a multi-language module)