"He bought some chocolate."
Translation:Prynodd o siocled.
Not quite. You can use it for 'some (few)' with a plural:
- Prynodd ei rai siocledi - He bought some (not many) chocolates
- Prynodd e rai o'r siocledi - He bought some (not many) of the chocolates
rhai is a sort of plural for un - ones. So for example y rheini (those, those ones) is a contraction of y rhai hynny.
However, there are a number of other ways of saying 'some of', 'not many', 'a bit of', 'a little of', 'a few of', 'several'.