How can I set the language (e.g. for date conversions)?

I am running openHab 2 on a Raspberry 2. I am using en_US as default locale on the pi. I would like to run openHab with locale de_DE. Is this possible and where can I set the locale?

I have tried to seht the LANG environment variable but this does not work. The openHab log file contains the following message:
LOCALE: no language is set, keep old: en_US

Such a feature has just been introduced by @maggu2810, but afaik, the documentation is still missing!

The documentation contains only the information how to get the locale.

The locale is set by the configuration admin and as an ESH service configuration (so visible in the Paper UI: Configuration, Services).

Thanks for the info, will try in the next days.