Avoid overloaded and default parameter functions here. Maybe:

* `loadDefaultTranslation()` - Loads the translation for `QLocale::system()`
* `loadTranslation(const QString &language)` - Load the translation for `language`

Both functions can then use a (non-exported, i.e. `SailfishAppPriv` member function) function to load the translations given a QLocale object.