One file per language
What a translation looks like in the repository and what happens when it is missing.
The main language has no suffix: 2.eine-datei-pro-sprache.md. Every other language gets its code before the extension: 2.eine-datei-pro-sprache.en.md.
A translation only needs the fields that differ. Everything else comes from the main file, for example the date and the authors.
The docs page "Languages" has more.