Try using C.UTF-8 locale

src/xfel_calibrate/calibrate.py

@@ -585,7 +585,7 @@ def run(argv=None):
     """ Run a calibration task with parser arguments """
     # Ensure files are opened as UTF-8 by default, regardless of environment.
     if "readthedocs.org" not in sys.executable:
-        locale.setlocale(locale.LC_CTYPE, ('en_US', 'UTF-8'))
+        locale.setlocale(locale.LC_CTYPE, ('C', 'UTF-8'))
 
     if argv is None:
         argv = sys.argv