improve translation and notificaiton displaying

Session/Meta/Translations/en.lproj/Localizable.strings

@@ -572,7 +572,8 @@
 "DISMISS_BUTTON_TEXT" = "Dismiss";
 /* Button text which opens the settings app */
 "OPEN_SETTINGS_BUTTON" = "Settings";
-"APN_Message" = "You've got a new message";
+"APN_Message" = "You've got a new message.";
+"APN_Collapsed_Messages" = "You've got %@ new messages.";
 "system_mode_theme" = "System";
 "dark_mode_theme" = "Dark";
 "light_mode_theme" = "Light";

Session/Notifications/UserNotificationsAdaptee.swift

@@ -127,11 +127,11 @@ extension UserNotificationPresenterAdaptee: NotificationPresenterAdaptee {
             let numberOfNotifications: Int
             if let lastRequest = notifications[notificationIdentifier], let counter = lastRequest.content.userInfo[AppNotificationUserInfoKey.threadNotificationCounter] as? Int  {
                 numberOfNotifications = counter + 1
+                content.body = String(format: NotificationStrings.incomingCollapsedMessagesBody, "\(numberOfNotifications)")
             } else {
                 numberOfNotifications = 1
             }
             content.userInfo[AppNotificationUserInfoKey.threadNotificationCounter] = numberOfNotifications
-            content.body = "\(numberOfNotifications) new messages."
         } else {
             trigger = nil
         }

SignalUtilitiesKit/Utilities/CommonStrings.swift

@@ -50,6 +50,9 @@ public class NotificationStrings: NSObject {
 
     @objc
     static public let incomingMessageBody = NSLocalizedString("APN_Message", comment: "notification body")
+    
+    @objc
+    static public let incomingCollapsedMessagesBody = NSLocalizedString("APN_Collapsed_Messages", comment: "collapsed notification body for background polling")
 
     @objc
     static public let incomingGroupMessageTitleFormat = NSLocalizedString("NEW_GROUP_MESSAGE_NOTIFICATION_TITLE", comment: "notification title. Embeds {{author name}} and {{group name}}")