Force __str__ methods of models to return str types instead of proxy types

CHANGELOG.rst

@@ -6,6 +6,14 @@ All notable changes to this project will be documented in this file.
 The format is based on `Keep a Changelog`_,
 and this project adheres to `Semantic Versioning`_.
 
+Unreleased
+----------
+
+Fixed
+~~~~~
+
+* ``Event.__str__`` returned a proxy type instead a string.
+
 `2.0rc2`_ - 2021-08-01
 ----------
 

aleksis/apps/chronos/models.py

@@ -976,7 +976,7 @@ class Event(SchoolTermRelatedExtensibleModel, GroupPropertiesMixin, TeacherPrope
         if self.title:
             return self.title
         else:
-            return _(f"Event {self.pk}")
+            return _("Event {pk}").format(pk=self.pk)
 
     @property
     def raw_period_from_on_day(self) -> TimePeriod: