Although I've heard cack-handed means left-handed, I've always used it to mean clumsy, in fact I called His Nibs that only today! I think it's because cack means crap in Welsh, at least according to my Granddad it does!
Granddad was from that generation of Welsh whose parents actively discouraged their children from learning the language even though it was their own first language.
Great-Granddad used to say "I speak three spokes, English, Welsh and rubbish".
Apart from cack and the usual Welsh everyone knows, the only other Welsh that crept into his vocabulary was "wedi mynd", used when something was unfixable. Mum told me it meant "gone west" actually wedi means past and mynd means go, does that mean the Long Mynd in Shropshire is Long Gone? !!