I came across this and was wondering if other terminology in artificial intelligence can be translated to Latin. Considering how deeply entwined the field is with science and philosophy, it is only fair for there to be proper scientific names for it like in biology :D
"Propagation", as it happens, comes directly from the Latin verb prōpāgō, -āre, -āvī, ātus. A nice word for "backwards" is rētrō. So putting those together, you'd get rētrōprōpāgātiō "back-propagation".
"Gradient descent" is harder. English "gradient" comes from gradior "to go"; the native Latin word for "slope" is clīvus, -ī. I think in this case I'd back-form from the English and get gradientia, -ae, "gradient". Then "to descend" is dēscendō, -endere, -endī, -ensus. So "the descent down a gradient" is dēscensus per gradientiam.