Created attachment 116030 [details] example multipart/multilingual message that can serve as a test case RFC 8255 defines multipart/multilingual for mail messages in multiple languages: https://tools.ietf.org/html/rfc8255 It would be nice to have support in kmail. There are two parts to this: correctly displaying them and being able to create them. Their implementation can happen separately, with the former being more straightforward (language choice based on application language trumped by kmail-specific setting).