Language of return receipts

The return receipts I get are usually in German (“Empfangsbestätigung”) as my peer sits in Germany. However, every now and then (at least once per day) it’s in English (“Return receipt”). This is of course not a big problem as it doesn’t impede the functionality of DeltaChat.
Still, out of curiosity, I’d like to know why this happens. Any ideas? Thanks!

Maybe your contact uses another device (e.g. desktop) where the language is set to English?

Could also be that it is a bug: UI start message sending before applying the translation.

Thanks! Sorry for the delay, but I needed some time for testing and making sure the solution we found is reliable.

We were able to rule out the influence of the language setting. Also, my contact uses DeltaChat only on one device.
However, we were able to identify the root of the problem:
The email identity my contact uses for DeltaChat they also had set up in Thunderbird, but as POP3 account instead of IMAP.
This had several effects:

  1. Although DC was able to display the message, Thunderbird fetched it from the server before DC could move it into the DeltaChat folder.
  2. In almost any case I got two return receipts.
  3. From time to time the return receipt was in English instead of in German.

By switching to IMAP in Thunderbird all seems to work fine now. Still, I’m wondering how the issues mentioned above are triggered by using POP3 in Thunderbird. :thinking:

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I have opened an issue describing why English MDNs may be sent sometimes:

Problems with POP3 connection removing the message and preventing move of the message to DeltaChat folder are solved since Android 1.27 (core 1.71.0), because the messages are no longer downloaded before they have reached their destination folder.

I am not sure why MDNs are sent twice in this case, this may have something to do with the failure to mark message as seen because it was already removed. Anyway, the code sending MDNs has been heavily reworked and decoupled from marking messages as seen on the server, so the bug is likely gone:

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