add singular translation string

src/i18n/strings/en_EN.json

@@ -806,8 +806,10 @@
     "Try scrolling up in the timeline to see if there are any earlier ones.": "Try scrolling up in the timeline to see if there are any earlier ones.",
     "Remove recent messages by %(user)s": "Remove recent messages by %(user)s",
     "You are about to remove %(count)s messages by %(user)s. This cannot be undone. Do you wish to continue?|other": "You are about to remove %(count)s messages by %(user)s. This cannot be undone. Do you wish to continue?",
+    "You are about to remove %(count)s messages by %(user)s. This cannot be undone. Do you wish to continue?|one": "You are about to remove 1 message by %(user)s. This cannot be undone. Do you wish to continue?",
     "For a large amount of messages, this might take some time. Please don't refresh your client in the meantime.": "For a large amount of messages, this might take some time. Please don't refresh your client in the meantime.",
     "Remove %(count)s messages|other": "Remove %(count)s messages",
+    "Remove %(count)s messages|one": "Remove 1 message",
     "Demote yourself?": "Demote yourself?",
     "You will not be able to undo this change as you are demoting yourself, if you are the last privileged user in the room it will be impossible to regain privileges.": "You will not be able to undo this change as you are demoting yourself, if you are the last privileged user in the room it will be impossible to regain privileges.",
     "Demote": "Demote",