"After Dewi Lingo went, I went home."
Translation:Ar ôl i Dewi Lingo fynd, es i adre.
I'm not a linguist, so can't give you a technical answer, but it's just something that some local dialects like to add to the positive forms of the past tense of the verb. It causes a soft mutation. So you can say: "Mi ddysges i Ffrangeg" and "Dysges i Ffrangeg". Both mean "I learnt French." To complicate things further, some people use the "mi" construction but then omit the "mi"! In that case, you still mutate, so "Ddysges i Ffrangeg", "Wnes is swper" etc.