There's a companion volume for Spanish learners, i.e. The publisher likely just tweaks a chapter or two for each specific target language, i.e. English Grammar for Students of $X.

The 'surprising specific' bit is in how concepts in German/Spanish map to their English equivalents. e.g. the German edition might try and show how English emulates declensions with prepositions, while the Spanish might explain how the auxilary verb 'have' has multiple uses covered by tener/haber.

I'm not a native Romance speaker but yes, knowing 'French shenanigans' would perhaps help understand the other - when I learned Catalan on duolingo (from Spanish), I made more blunders in my rusty Spanish than in mistakes in the Catalan I was trying to learn!