All true. Lothar is not like the characters Stepin Fetchit played in 40s movies. I can accept his substandard English; recently I've heard Korean immigrants have as much (or more trouble) with what is a tricky language. The way he's afraid of ghosts and other supernatural events is compensated by the fact he's sure not intimidated by anything made of flesh and blood.
Lee Falk said he intended for Mandrake and Lothar to complement each other. Mandrake would be mental power and Lothar physical power. Yin and yang, and in fact Lothar does dive into danger all the time to pull Mandrake out of a mess.
There was one story where Lothar's father dies and he is called to take the throne. Aside from an exciting battle against a neighboring nation, Lothar finds all his time taken up with tedious boring legal disputes he must resolve. Then there's the harem of obese women his father left... Mandrake does not press Lothar to come with him. He says they've been great friends and he'll miss him, but he leaves Lothar to make up his own mind.