Use toml instead of json for settings.

pyproject.toml

@@ -12,6 +12,7 @@ license = { text = "LGPL-2.1-or-later" }
 dependencies = [
     "pygobject>=3.18",
     "pluggy",
+    "tomlkit",
     "brlapi; extra == 'braille'",
     "python-speechd; extra == 'speech'",
     "piper-tts; extra == 'piper'",