Best place for date/time setting

[markr]

I am writing some small enhancements for the Forum Made Easy module. Besides clean URL's, I want to make the date-time format in the proper locale. But it doesn't seem to be a setting in the core (strange!). Also, I don't like the idea that it is a setting local for each module (the News module does have a date-format setting).

I consider using lang/*.php for this, as these are locales in fact. For example:
  $lang['date_time_format'] = '%m-%d-%y %m:%h %a'; // or something that works

Anyone an opinion what the best way is for storing the date/time format string?

Mark