Use system default encoding when normalising locale

calendarweek/util.py

-from locale import locale_alias, locale_encoding_alias
+from locale import getpreferredencoding, locale_alias, locale_encoding_alias
 from typing import Optional
 
 
@@ -6,5 +6,7 @@ def normalise_locale(loc: str, enc: Optional[str] = None) -> str:
     loc = locale_alias.get(loc, loc)
     if enc:
         enc = locale_encoding_alias.get(enc.replace("-", ""), enc)
-        loc = loc.split(".")[0] + "." + enc
+    else:
+        enc = getpreferredencoding()
+    loc = loc.split(".")[0] + "." + enc
     return loc

pyproject.toml

 [tool.poetry]
 name = "calendarweek"
-version = "0.4.0"
+version = "0.4.1"
 description = "Utilities for working with calendar weeks in Python and Django"
 authors = ["Dominik George <nik@naturalnet.de>", "Jonathan Weth <git@jonathanweth.de>"]
 license = "MIT"