Owh, I just knew and realised it today. **Thanks to the thread's title by the way.
"Slainte Mhath" is equal to cheers in Scotland.
The term Slàinte Mhath (Pronounced Slanj-a-va) is actually both Irish and Scots Gaelic. The way the phrase is pronounced is the same for both languages, however the way it is spelt differs subtly. The Irish spell it Slàinte Mhaith.
The phrase translates to "Good health" in both dialects, and if you want to respond to this using Scots Gaelic, you would say, "do dheagh shlainte" meaning "to your good health."