Rollo had conquered the French northern coast and wrecked so much shit the French king just offered to make him a vassal, and give him more land in the process, if he protected the land he'd taken from other Viking raiders. This area would develop a hybrid culture from the mixing of the Germanic invaders and French population.

English, already a bastardized Germanic language, combined from the spoken languages of Germanic invaders who would come to be known as Anglo-Saxons and the native population, got further hybridized by a French Viking who actually spoke a French-Germanic dialect known as Norman.

Tl;Dr

Sea Germans hate linguistic purity, and English's problems are all their fault.