Can a possible translation be also "I had dinner with you?" I mean, it means the same.
"dinner" as a translation of swper is fine but "I had" would be more "Ces i/Cefais i" whereas "Bwytais" only equates to ate.
So would 'Bwytais i cinio gyda chi' be incorrect?
Hmm I wouldn't say so except ut would have to be "Bwytais i ginio...?.