[Feature Request]: Add datetime formatting options for different locales

[benjaminhansen]

I've seen this need specifically in the Mails UI, but it could exist elsewhere in Herd too. It seems that all of the date/time stamps are hardcoded to a specific format (d.m.Y, h:m), and I haven't found a way to change it.

It might be helpful to add a configuration option to change that format according to whatever locale the developer is working in.

Even if it was just ISO 8601 formatted by default.