Proposed changes

Add philipp15b/php-i18n i18n.class.php via composer:

$ composer require philipp15b/php-i18n

and convert current localizations to JSON.

Tasks

• Require class
• Change localization folder to l10n
• Convert php-arrays to json
• Implement in all applicable pages:
  • script.php
  • impressum.php
  • privacy-policy.php
  • offline.php
  • main.php
• Debate restructuring language-code named folders
• Edit README!
• Push & publish