An advantage of learning German is that Germany is doing well economically.
I would translate it as
Ein Vorteil vom Deutschlernen ist, dass es Deutschland wirtschaftlich gut geht.
Is the comma in front of "dass" correct or not?
You always have to put a comma in front of the dass conjunction because it indicates a dependent clause which cannot stand for itself (including the conjunction).
The only exception is when the clauses are actually compound by conjunctions that doesn’t require a comma, like und and oder:
Also when the clauses are in reversed order you have to put a comma:
… or in your case:
The reversed form is often used when you want to enumerate different statements: