Answer:
This is the Scots language. It means 'until all the seas go dry' i.e. until the ends of time.
Not to be a jerk, but--technically, no. "'Till all the seas gang dry" is of a dialect and not a distinct language in and of itself.
Strictly speaking, there's no such thing as the "Scots language." There's Lallans and Braid, but they're dialects of English, and there's Scots Gaelic, but that--obviously--is Gaelic and not English.
PS: Yes, there are other dialects too (Highland, Coastal, etc.), but you get the point.