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Lacre frontend (the interface used to upload, verify and delete keys) communicates with the backend (the job actually importing keys and encrypting messages with them) via database.
This could be changed by moving all database accessing-code to the backend and exposing a simple API for the frontend to call. This API could be a Unix or TCP socket, or maybe some queue to send messages to.
We could use gettext to translate Lacre messages to different languages (for example Spanish).
See Alembic
Instead of using our own wrapper for GnuPG we should consider using something more thorough, like pretty-bad-protocol. (However, this project seems to be inactive since 2018…)