Depending on locale, darktable refuses to tether if lens aperture is reported as 0

Is there an existing issue for this?

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

Describe the bug

Canon EOS 6DMKII.
With an "ordinary" lens attached, tethering works independent of the locale.
With a lens which reports aperture 0 (slide duplicator in this case), tethering fails with the default German locale but works when I force en_US locale with LC_MESSAGES=en_US.UTF-8 darktable.
Confirmed with both darktable 5.4.1 (distro build) as well as darktable 5.6.0 (AppImage).

Steps to reproduce

1. Connect camera and turn on. It shows up under "import".
2. "Mount camera" ("Kamera verbinden") from Darktable
3. Hit "Tethering"
4. With German locale: Camera is unmounted after a few seconds, error message talks about aperture property not being set

Expected behavior

Open tethering module

Logfile | Screenshot | Screencast

https://github.com/user-attachments/assets/a62011b4-3eef-4b4c-aadb-f71fdb2e13fc

Commit

No response

Where did you obtain darktable from?

distro packaging

darktable version

5.4.1

What OS are you using?

Linux

What is the version of your OS?

Fedora 44

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

Start by reproducing the tethering failure on Linux with the German locale and compare it with LC_MESSAGES=en_US.UTF-8 darktable, using the Canon EOS 6DMKII and a lens reporting aperture 0. Trace the tethering path that reports the aperture-property error; done means tethering opens successfully under the German locale without breaking ordinary lenses.