feat: do not reveal sender's language in read receipts (#5802)

while adapting strings for the recent change about read receipts,
https://github.com/deltachat/deltachat-core-rust/pull/5712 , it turns
out in discussions eg. at
https://github.com/deltachat/deltachat-android/issues/3179 that
untranslated english for the read receipts seem to be sufficient or even
better:

- do not reveal the sender's language
- unexpected languages are confusing - even if you chat in english, you
may get Chinese read receipts
- many clients do not show the text anyways, iirc, eg. Outlook display
the read receipts in context, and Delta Chat of course as well
- afaik, we're leaving comparable `multipart/report` untranslated as
well (sync, but also webxdc updates are practically english only)
- less code, fewer translations needed :)

deltachat-ffi/deltachat.h

@@ -6650,6 +6650,8 @@ void dc_event_unref(dc_event_t* event);
 /// "Message opened"
 ///
 /// Used in subjects of outgoing read receipts.
+///
+/// @deprecated Deprecated 2024-07-26
 #define DC_STR_READRCPT                   31
 
 /// "The message '%1$s' you sent was displayed on the screen of the recipient."
@@ -6657,7 +6659,7 @@ void dc_event_unref(dc_event_t* event);
 /// Used as message text of outgoing read receipts.
 /// - %1$s will be replaced by the subject of the displayed message
 ///
-/// @deprecated Deprecated 2024-06-23, use DC_STR_READRCPT_MAILBODY2 instead.
+/// @deprecated Deprecated 2024-06-23
 #define DC_STR_READRCPT_MAILBODY          32
 
 /// @deprecated Deprecated, this string is no longer needed.
@@ -7376,11 +7378,6 @@ void dc_event_unref(dc_event_t* event);
 /// Used as info message.
 #define DC_STR_SECUREJOIN_WAIT_TIMEOUT 191
 
-/// "The message is a receipt notification."
-///
-/// Used as message text of outgoing read receipts.
-#define DC_STR_READRCPT_MAILBODY2 192
-
 /// "Contact". Deprecated, currently unused.
 #define DC_STR_CONTACT 200
 

node/constants.js

@@ -267,7 +267,6 @@ module.exports = {
   DC_STR_REACTED_BY: 177,
   DC_STR_READRCPT: 31,
   DC_STR_READRCPT_MAILBODY: 32,
-  DC_STR_READRCPT_MAILBODY2: 192,
   DC_STR_REMOVE_MEMBER_BY_OTHER: 131,
   DC_STR_REMOVE_MEMBER_BY_YOU: 130,
   DC_STR_REPLY_NOUN: 90,

node/lib/constants.ts

@@ -267,7 +267,6 @@ export enum C {
   DC_STR_REACTED_BY = 177,
   DC_STR_READRCPT = 31,
   DC_STR_READRCPT_MAILBODY = 32,
-  DC_STR_READRCPT_MAILBODY2 = 192,
   DC_STR_REMOVE_MEMBER_BY_OTHER = 131,
   DC_STR_REMOVE_MEMBER_BY_YOU = 130,
   DC_STR_REPLY_NOUN = 90,

src/mimefactory.rs

@@ -454,7 +454,7 @@ impl MimeFactory {
                 };
                 stock_str::subject_for_new_contact(context, self_name).await
             }
-            Loaded::Mdn { .. } => stock_str::read_rcpt(context).await,
+            Loaded::Mdn { .. } => "Receipt Notification".to_string(), // untranslated to no reveal sender's language
         };
 
         Ok(subject)
@@ -672,7 +672,7 @@ impl MimeFactory {
                         })
                 }
             }
-            Loaded::Mdn { .. } => self.render_mdn(context).await?,
+            Loaded::Mdn { .. } => self.render_mdn()?,
         };
 
         let get_content_type_directives_header = || {
@@ -1400,7 +1400,7 @@ impl MimeFactory {
     }
 
     /// Render an MDN
-    async fn render_mdn(&mut self, context: &Context) -> Result<PartBuilder> {
+    fn render_mdn(&mut self) -> Result<PartBuilder> {
         // RFC 6522, this also requires the `report-type` parameter which is equal
         // to the MIME subtype of the second body part of the multipart/report
         //
@@ -1426,16 +1426,15 @@ impl MimeFactory {
             "multipart/report; report-type=disposition-notification".to_string(),
         ));
 
-        // first body part: always human-readable, always REQUIRED by RFC 6522
-        let message_text = format!(
-            "{}\r\n",
-            format_flowed(&stock_str::read_rcpt_mail_body(context).await)
-        );
+        // first body part: always human-readable, always REQUIRED by RFC 6522.
+        // untranslated to no reveal sender's language.
+        // moreover, translations in unknown languages are confusing, and clients may not display them at all
         let text_part = PartBuilder::new().header((
             "Content-Type".to_string(),
             "text/plain; charset=utf-8; format=flowed; delsp=no".to_string(),
         ));
-        let text_part = self.add_message_text(text_part, message_text);
+        let text_part =
+            self.add_message_text(text_part, "This is a receipt notification.\r\n".to_string());
         message = message.child(text_part.build());
 
         // second body part: machine-readable, always REQUIRED by RFC 6522

src/stock_str.rs

@@ -80,9 +80,6 @@ pub enum StockMessage {
     #[strum(props(fallback = "Fingerprints"))]
     FingerPrints = 30,
 
-    #[strum(props(fallback = "Return receipt"))]
-    ReadRcpt = 31,
-
     #[strum(props(fallback = "End-to-end encryption preferred"))]
     E2ePreferred = 34,
 
@@ -440,9 +437,6 @@ pub enum StockMessage {
         fallback = "Could not yet establish guaranteed end-to-end encryption, but you may already send a message."
     ))]
     SecurejoinWaitTimeout = 191,
-
-    #[strum(props(fallback = "This message is a receipt notification."))]
-    ReadRcptMailBody = 192,
 }
 
 impl StockMessage {
@@ -795,16 +789,6 @@ pub(crate) async fn finger_prints(context: &Context) -> String {
     translated(context, StockMessage::FingerPrints).await
 }
 
-/// Stock string: `Return receipt`.
-pub(crate) async fn read_rcpt(context: &Context) -> String {
-    translated(context, StockMessage::ReadRcpt).await
-}
-
-/// Stock string: `This message is a receipt notification.`.
-pub(crate) async fn read_rcpt_mail_body(context: &Context) -> String {
-    translated(context, StockMessage::ReadRcptMailBody).await
-}
-
 /// Stock string: `Group image deleted.`.
 pub(crate) async fn msg_grp_img_deleted(context: &Context, by_contact: ContactId) -> String {
     if by_contact == ContactId::SELF {