Using api.php?action=query&meta=userinfo&uiprop=rights|hasmsg I get
information about new message.
Now I can read it using api, but that doesn't flag the talk page as
read.
I tried action=setnotificationtimestamp as someone suggested but later I received a response that it's broken and needs fix. So once it's fixed just close this.
Version: 1.23.0
Severity: enhancement