Date time format does not respect locale.

[MarekKnapek]

Prerequisites

• [X] I am reporting a problem, not asking a question (for questions, go to Discussions).
• [X] I have consulted the user guide.
• [X] I have confirmed that I'm running the current version and the problem persists there (note the version number in fine print next to the add-on name on addons.thunderbird.net and compare it to the version number listed in the add-on details opened from the Add-ons page in Thunderbird; if you've got an old version, click the gear icon and select "Check for Updates").
• [X] If I'm having an issue with date-parsing confusion, I've read the section about that in the user guide and I still think this is something different.
• [X] If I'm having an issue with messages not being delivered, I've followed the troubleshooting steps in the user guide and it's still an issue.

Describe the bug

I see American style date time format even if I live in Europe and both my Windows and Send Later are set to display ISO-8601 date time format.

How to reproduce

• Install Windows.
• Set Windows date time format to ISO-8601 aka 2024-03-01 06:01.
• Set Send Later date time format to ISO-8601 aka 2024-03-01 06:01.
• Send Later does not respect my settings and displays date separated by slashes (instead of dashes) and AM/PM (instead of 24h format).

Expected behavior

• Respect Windows settings.
• Send Later has its own settings, but it does not respect it iether.

Additional context

Windows Server 2022 x64 with all updates, Thunderbird with all updates, Send Later latest greatest version.

Operating System

No response

Operating System Version

No response

Thunderbird version

115.8.0 (64-bit)

Send Later start-up string

No response

[jikamens]

Send Later doesn't have any control over the format used by the date-picker. It's a widget provided by Thunderbird, and the Thunderbird code decides how to format and display it. I'm pretty sure it's the same code that's used by Firefox. If you want to file an enhancement request at https://bugzilla.mozilla.org/ about making the date-picker more sensitive to the OS date formatting settings, you are welcome to do that, but I can't do anything about it in Send Later so I'm going to close this issue here.