Add Catalan translation

[welpo]

Checklist

• All new and existing tests are passing
• (If adding features:) I have added tests to cover my changes
• (If docs changes needed:) I have updated the documentation accordingly.
• I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)
  

What changes does this Pull Request introduce?

Adds Catalan translation.

Why is this necessary?

Over 9 million people speak Catalan :)

[welpo]

I'm not sure about adding an entry to CHANGES.rst. Should I add a "New features" section inside "TBD" like this?

- TBD

New Features
^^^^^^^^^^^^

- Add Catalan localisation (`#966`_, welpo)

Bugfixes & Improvements
^^^^^^^^^^^^^^^^^^^^^^^

- Python 3.11 support (`#832`_, l33tname)
…

[ix5]

Please squash the two commits into one, otherwise LGTM.

Thank you for your contribution!

[welpo]

Done!

Should I update the CHANGES.rst file as mentioned above?

[ix5]

Done!

Should I update the CHANGES.rst file as mentioned above?

Yes, please.

[welpo]

Done!

[ix5]

Great, thank you! Merged.