Am I completely off base here or is this mumbling equals laziness thing something unique to the English language? I'm German and I really wasn't aware of this

Am I completely off base here or is this mumbling equals laziness thing something unique to the English language? I'm German and I really wasn't aware of this association at all. I associate mumbling with shyness … and that's about it. And what's more that association to laziness seems positively weird and non-sensical to me.