TYPO3 Core

The two formats use two different ways of php (1. DateFormat->format(); 2. strftime). The first one does only use English (http://php.net/manual/en/datetime.format.php#refsect1-datetime.format-notes) and the second one is localizable. So I think to localize both would be breaking to php in some way.

The second part about defining a default format would be cool :) (And yes I know the current default is Y-m-d), but it would be great to set something like this within typoscript.

Would it be possible to use translation in both ways?

No, unfortunately not. One method uses date() the other uses strftime() and those two work quite differently. The date() format can't be used in strftime() and vice versa.

Also it would be great to define a default date format.

You should definitely do this using a {settings.foobar} variable. There are a few hinges preventing use of a default date format (unless you can indicate a cross-platform safe system option?). The issue is that it's an edge we would rather want to avoid - defining default behaviors of ViewHelpers using TypoScript. That being said, I will definitely consider a feature that would let you override default argument values - but I'm afraid you have to be a bit patient about that one; it would have to be in the standalone Fluid that won't be available as dependency until TYPO3 8. Once that hits you'll have a way to do this via the View (subsequently via the controller, possibly configured through TypoScript as a TYPO3-specific Fluid feature).

Thank you very much for the detailed answers.

I coundn't find any information about using strftime with format.date.
Maybe someone could add some information about localisation with strftime.
Also it would be great if someone could add this info to the Extbase and Fluid FAQ:
[[https://wiki.typo3.org/Extbase_und_Fluid_FAQ#How_can_I_render_localized_dates.3F]]