I recently came across this card while studying Spanish on the lingvist website:
If I were to literally translate this sentence I would get something like: In (my) life I have seen such a thing.
So why does the translation in the card contain a negation? When I tried Google Translate it confirmed my literal translation. Then I tried Reverso Dictionary which confirmed the translation in the card, but described the Spanish phrase as an expression. Further down on the reverso.net page were listed some variants of the phrase which did contain negations (in Spanish) and were less confusing in my view.
Perhaps some additional explanatory information could be added to the card to help people like me who find the Spanish expression confusing?