Please add another parameter giving the number of messages left by $1 - reason given below in the last section. (Other languages may ask for the total number of messages as well)
This message is generally complicated due to the 99+ cases. I am asking myself: does it have to be so?
I am not 100% certain about English, but if there is only 1 who left several messages, does it not have to be "messages" instead of "a message"? If there are several who left 1 message each, does it not have to be "a message each"? If many messages were left, does it not have to be "messages" instead of "a message"?
In German, you can always say "a message", no matter how many ones left how many messages, since it automatically implies "a minimum of 1 message".
In Colognian, we must use "a message" for "1 originator left 1 message" and "several originators left 1 message each", and we must use "messages" in all other cases. (Fortunately, we have no zero case here) That is, without more information about the number of messages left, this text cannot be properly translated. Luckily, in this context, I believe that we can do with the number of messages by the named originator (1 or more) alone, since the list of left messages is not visible together with the counts, so we can safely assume that using "messages" in all cases but "1 originator left 1 message" is not going to be realized as a self-contradiction by readers.
See also("$1 and $2 others left a message on your talk page.").
Filed as phab:T125264. Very sorry about the long delay. (I'm not sure whether it's practical to get the exact number of messages (or rather, how much extra backend code and processing that would take) hence filed on phabricator for the devs to contemplate).