"Dach chi eisiau llefrith?"
Translation:Do you want some milk?
This could also be "Do you want some milk?". Because Cymraeg has no concept at all of indefiniteness, any indefinite articles (and their substitutes) are omitted. The English word some can be used as a plural indefinite article (a/an). Compare "I want an apple" and "I want some apples" (but "I want apples" also makes sense). This use of some goes untranslated in Welsh just as the English a/an does.
Ydach chi isio llefrith? - Do you want (some) milk? (North)
Ydych chi eisiau llaeth? - Do you want (some) milk? (South)