How well can an adult learn a foreign language?

I found German more difficult than French (had both in high school).

The frame of English is Gemanic, true, but something like 50 percent of the vocabulary is Romance- or Latin-derived, and is more similar to French than German. English word order is more similar to French than it is to German. And German has three genders, while French only has two.

That being said, you’ve a leg up because you already have experience in German and it will be easier the second time around.