I propose more flexibility regarding to disappearing messages. Sometimes contacts take long time to reply, or you want to make appointments in advance, and so having option for longer then 5 weeks is nice for these cases.
WhatsApp has option for 90 day disappearing messages, which is suitable for these cases.
Signal also has option for custom disappearing time, so user can set number of days or weeks if the default time is not suitable. The UI feels clean.
Maybe Delta Chat can also have option like 90 day disappearing messages and custom disappearing time?
For days highest number is 6 and for weeks highest number is 4, so you cannot even set it to 5 weeks or 15 days with these settings. Translating resulting info messages will also become much more difficult.
You can turn on “disappearing messages” in the settings of a chat, at the top right of the chat window, by selecting a time span between 1 minute and 5 weeks.