This consolidates the places where a default language has to be set.
- Removed import of the 'userService' package into the 'languages' util
package
This was required to prevent a cyclic import between the two packages.
- Added a 'UserRetriever' interface to read the language setting of users
inside the 'languages' package
- Fixed an error in the spanish and chinese translation file
- Refactored reading the translation files
Instead of ignoring errors in the non-default language files
the error will now be returned and the remaining files will
not be loaded.
- Added a unit test to check if all translation files are valid
- Added an i18n config to specify the translations dir and the
default language