I don't know who feasible this would be but for the sake of creating a Muslim Germanic culture here's mine. North African Vandals defeat the Roman reconquest of North Africa during the Vandal War. The Vandal kingdom survives and thrives. Let's say nearly a hundred years later, the Vandals are among the first to convert to Islam. Following a top to bottom conversion beginning with the Vandal king and nobility down to the commoners. The Vandals establish a powerful Islamic kingdom in North Africa known as the Vandal Caliphate with its capital in otl Algeria or Tunisia.
Meanwhile political divisions causes Visigothic Spain to split into two factions between Roderic on one side and Achila on the other. Long story short, Achila invites the Vandals to help him against Roderic. The Vandals, who are relatively new converts to Islam are enthusiastic for conquest and to spread the faith, eagerly oblige.
Right about the same time as otl Roderic is killed around 711 in a battle with the Vandals and pretty soon Visigoth Spain becomes Vandal Spain ruled by a Vandal Caliphate.
al vandalusia is a tl i never know i wanted to but now i need to.