On i18n/en.json:
"echo-category-title-article-reminder" (This is a short title for notification category.\n\nUsed in a list of options under the heading {{msg-mw|Prefs-echosubscriptions}} in Special:Preferences. As far as I can see this always needs to be a plural for an unspecified number.\n\nIt used to be used as <code>$1</code> in {{msg-mw|Echo-dismiss-message}}, but this message is no longer used, apparently.\n\nParameters:\n* $1 - number of messages, for PLURAL support\n{{Related|Echo-category-title}}): "Page {{PLURAL:$1|article-reminder|article-reminders}}",
"echo-pref-tooltip-article-reminder" (This is a short description of the article reminder user notification category\n{{Related|Echo-pref-tooltip}}): "Notify me about this article when I asked.",
"notification-header-article-reminder" (Message for page-reminder notification. Parameters:\n* $1 - the formatted username of the user who requested the reminder. \n* $2 - the username for GENDER\n* $3 - the formatted page title of the article the user requested): "An article {{GENDER:$2|you}} have requested to be reminded about is at <strong>$3</strong>",
"notification-link-article-reminder" (Label for the link to the article the user requested to be reminded about): "View article",
"echo-reminder-popup-main-title" (Title for the page reminder popup): "Set a reminder about this page",
"echo-reminder-comment-input-placeholder" (Placeholder for the page reminder comment inptut): "Review this page...",
"echo-reminder-timestamp-title" (Lable for the page reminder choosen timestamp): "When",
"echo-reminder-timestamp-input-placeholder" (Placeholder for the page reminder timestamp input): "Pick a date",
"echo-reminder-tomorrow" (Lable for one of the suggested timestamp for the page reminder): "Tomorrow",
"echo-reminder-next-week" (Lable for one of the suggested timestamp for the page reminder): "Next week",
"echo-reminder-next-month" (Lable for one of the suggested timestamp for the page reminder): "Next month",
"echo-reminder-cancle" (Lable for cancle button in the page reminder popup): "Cancle",
"echo-reminder-approve" (Lable for approve and create an page reminder): "Create reminder"
We'll also put the notification type on Beta Cluster soon ( {T169354} ) which should help with this.