I am filling a form with text and checkbox fields. Text values may contain german characters.
If a checkbox is programmatically selected then subsequent fields are corrupted.
It might not be a pypdf fault, see viewers comparison in caveats below.

vs.

Caveats:

• if the corrupted field gets focus the displayed text is correct ( back to incorrect when the focus is lost):
  

• case reproduced in Adobe Acrobat Reader

• Chrome viewer shows correct characters:
  

• Firefox viewer shows incorrect characters (even in the first field) regardless of checkbox:
  

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
Windows-10-10.0.19045-SP0

$ python -c "import pypdf;print(pypdf.__version__)"
3.12.2

Code + PDF

This is a minimal, complete example that shows the issue:

from pypdf import PdfWriter

writer = PdfWriter()
writer.append("./visa-form.pdf")

writer.update_page_form_field_values(
    writer.pages[0],
    {
        '1 Surname': 'Zürich', 
    #    'Check Box 9.1': '/Ja',  # skip or not
        '9': 'Zürich'
    }    
)

with open("./zurich-test.pdf", "wb") as output_stream:
    writer.write(output_stream)
    output_stream.close()

visa-form.pdf
zurich-test-no-checkbox.pdf
zurich-test-with-checkbox.pdf

Traceback

TODO