locale.strxfrm raising an error on characters incompatible with the locale.

[oussjarrousse]

after rednotebook reads all the day files, and when it is trying to sort categories, it raises an error.

After some investigation I found out that the error is related to locale.strxfrm in line 516 in journal.py:

    @property
    def categories(self):
        return sorted(
            set(itertools.chain.from_iterable(day.categories for day in self.days)),
            key=locale.strxfrm,
        )

What I think is happening is that locale.strxfrm does not accept characters that are incompatible with the locale.
For example, my locale is en.US.UTF-8. For example: locale.strxfrm("عربي") will raise an error

Traceback (most recent call last):
  File "/Users/ouss/Documents/workspace/rednotebook/rednotebook/journal.py", line 624, in <module>
    main()
  File "/Users/ouss/Documents/workspace/rednotebook/rednotebook/journal.py", line 606, in main
    journal = Journal()
  File "/Users/ouss/Documents/workspace/rednotebook/rednotebook/journal.py", line 238, in __init__
    self.open_journal(journal_path)
  File "/Users/ouss/Documents/workspace/rednotebook/rednotebook/journal.py", line 401, in open_journal
    self.frame.categories_tree_view.categories = self.categories
  File "/Users/ouss/Documents/workspace/rednotebook/rednotebook/journal.py", line 514, in categories
    return sorted(
OSError: [Errno 22] Invalid argument

What I wish to happen, is that categories are sorted regardless of the characters type or locale.

[jendrikseipp]

Do you know what needs to be changed to fix this?