Localization with locales
This is an epic to group all tasks related to introducing locales as the basis for localization, effectively superseding the concept of a "default language" in the pagetree.
The concept still needs to be further discussed. The first implementation should only provide the current featureset, that is, the translations still have to be based on a language that is defined as the default for the current pagetree. This can later on be replaced with something else.
A draft for the concept is discussed at https://docs.google.com/document/d/12zhMTMBQUFqY64TTnHx8PoCNWslY4vRWsrFDtpm_X14/edit?usp=sharing
There is a draft implementation of locales for files, which was never integrated. Take a look at https://github.com/andreaswolf/TYPO3.CMS/tree/feature/file-localization-locales.