Support locale aware date formats

[DSiekmeier]

Is your feature request related to a problem? Please describe.
Entering reading dates currently has to have the format [day].[month].[year], that is, the separator has to be a dot. This is only reasonable for german speaking countrys (?).

Describe the solution you'd like
The minimum feature set should be to accept also other separators. But actually the dates should be entered as the user is used to it.