2019-11 We asked WPML

Our question

Are all translations stored in po/mo files which we can copy using ftp, or are they stored in the database?

Answer from WPML

Hi Adam, there are 2 big areas but both require database access to some extent:

1) strings in themes and plugins: these are stored in mo/po files unless you want to modify them with our String Translation plugin. In which case they would be stored in the database. Here you have a better explanation of how string translation currently works:
https://wpml.org/2019/08/wpml-4-3-beta-1-with-much-faster-string-translation/
2) posts and pages: these translations are stored in the database, just like the originals.
We use an extra table to connect an original post to its translation. You can read more about this structure over here:
https://wpml.org/documentation/support/wpml-tables/