Is it permissible for me to cook and serve meat that has not been slaughtered [according to Islamic rites] in my restaurant in Germany if my customers are non-Muslims, or is it forbidden for me to touch this meat?

It is not permissible to cook meat that has not been slaughtered Islamically, even if it is for non-Muslims, because doing so is an aid to sin and transgression. Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty" (Al-Ma'idah: 2).