Read it in English, send it in theirs

Translate a customer's message into English without losing their words, and write your reply in English while sending it in their language.

Translate on a message — the English appears underneath the original, labelled with the language it came from. Their words stay on screen.
Writing back — see your English and their language side by side, then pick one. Send always sends what is in the box.
It only offers a language the conversation has shown — an all-English inbox sees nothing new.
Keep typing and the preview clears itself, so it can never paste over a newer sentence.