"Oidhche mhath, tìoraidh an-dràsta."
Translation:Good night, bye just now.
It's a Scots usage. Cheerie-bye as in cheerio! And slainte actually means health, even though it's commonly translated as cheers! - it's really a contraction of "your health!" The standard reply is "slainte mhath!" which is "your good health!", which doesn't make a lot of sense if you're thinking of slainte in the sense of cheers! (Slainte! with the reply "Slainte mhath!" is in common use in Scotland even among non-Gaelic speakers.)