Tag tree separating with polish letters

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

My tag tree was separated in the "collections" module. Everything was displayed correctly in "tagging", but in "collections" I would use some parent tags displayed twice instead of just once. It took me a while to realise that this was because some of the tags used polish characters (ą, ę, ć, ń, ó, ś, ż, ź, ł). After I corrected this issue - stopped using polish characters when tagging - the problem disappeared. I have recreated it for the purpose of creating the attached screenshot.
This was quite annoying for browsing large collections through tags, but otherwise the program seemed to have worked properly.
If fixing this issue is not possible currently I would suggest adding a warning of using national characters in order to make users avoid them.

Steps to reproduce

1. Create a parent tag
2. Add two children to the tag: one using polish letters, the other one without them
3. Attach these two tags to photos
4. Collections should now display the parent tag twice, once for every child tag.
5. All children tags with polish characters will be grouped under one parent and vice versa.

Expected behavior

Darktable should display all children tags under one parent regardless of characters used

Logfile | Screenshot | Screencast

darktable-log.txt

Commit

No response

Where did you obtain darktable from?

darktable.org / GitHub release

darktable version

5.6.0

What OS are you using?

Windows

What is the version of your OS?

Windows 10 22H2

Describe your system

No response

Are you using OpenCL GPU in darktable?

None

If yes, what is the GPU card and driver?

No response

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response

Reproduce the issue in the Collections module using a parent with one child tag containing Polish characters and one without, then compare the result with the Tagging view. Start by examining how Collections groups and displays tag-tree parents, using the attached screenshot and logfile for context. Done means all children appear under one parent regardless of the characters used.