Feature/i18n

Please do not yet merge this, the task is mostly completed, but there are still some minor issues:

* [ ] Return default language values, if a value is not available in the requested language
* [ ] The build is currently failing in OpenJDK 6 due to a [MissingResourceException](https://travis-ci.org/autermann/SOS/jobs/28308622#L4710)
* [ ] There are still some issues regarding ISO 3166-1 alpha-3 handling