Sorry to confuse you, the UX is kinda wonky. Whatever flag you choose is what determines your language for both outgoing and incoming messages. So if you choose

Sorry to confuse you, the UX is kinda wonky. Whatever flag you choose is what determines your language for both outgoing and incoming messages. So if you choose German, that is what will determine the "From" language to translate on your outgoing messages and the "To" language for incoming.