Further improved i18n stuff - added dozens of missing i18n/Gettext syntax etc

Further improved i18n stuff:
- added dozens of missing i18n/Gettext syntax including the country list,
- added 2 new countries (Serbia, Montenegro),
- corrected 1 country (Timor-Leste/ East Timor),
- expanded and updated default .po/.pot file for translators,
- completed and improved packaged German translations (informal version) for current Github master branch

Thanks, Dave :)