[lagrange77]

For example an additional drop-down menu with common date string formats, where the first entry is the OS default for the given locale.

Additionally one could add a text label, which displays an example date formatted by the currently selected choice.

[Maelcum]

See? It's really not that hard, you just need to switch the perspective for a minute: what would I prefer if I were a user? Hiding the complexity from the user is one step forward to a better UI.