- The existing common.i18n library contained code for core and theme translations
- There is some shared logic and some theme-specific logic, and the theme-specific logic has dependencies we don't want in lib/common
- This refactor introduces an I18n base class that does all the main shared logic, with no dependencies on other parts of the codebase
- ThemeI18n then extends this logic, and replaces the functions it needs to handle differently and adds it's dependencies on config and settingsCache
- The class has several methods broken down into smaller pieces to make it easier to extend only the necessary parts
- The class also encapsulates all of its logic, without external functions or variables
- The function loadThemeTranslations becomes the 'init()' function overridden in themeI18n.
