> Outside of Germany, what exact benefit does the German language get you?

German is also official language in Austria, Switzerland and Luxembourg. In many neighbouring countries it is also often well-understood and/or there exist language minorities.

> English is the global lingua franca

From my professional experience I can tell that depending on the countries or persons from countries that you deal with, Spanish, French, Russian or Chinese can be much more important than English.

So, calling English the global lingua franca is in my opinion rather based on a selection bias on specific countries.