"Do you want some chocolate?"
Translation:Dych chi eisiau siocled?
In this context it can be. Welsh has no indefinite article like the English 'a/an' nor does it have an equivalent of an indeterminate 'some' - just a noun on its own can include these meanings.
There are words for 'some' when it means 'a little bit', 'some (of a greater number/amount', 'some sort of' and so on.
Dw i eisiau siocled can mean that I want 'chocolate', 'a chocolate' or 'some chocolate'. In a negative sentence or a question siocled could be also translated as 'any chocolate': dw i ddim eisiau siocled - 'I don't want any chocolate'.