Translation:These snakes are striped, but those are spotted.
'those ones' is not standard (formal) English. Standard is just 'those'. In other words, 'those' can be a pronoun as well as an adjective/determiner.
For example, compare:
1. Those ones over there are on sale.
2. Those over there are on sale.
You will hear 1 from time to time, but 2 is what is taught to and used by most speakers most of the time.
Lexico's entry has five examples with "ones" as a pronoun to refer to things, and fifteen with "ones" to refer to people. ( https://www.lexico.com/definition/one ) It is standard, not even colloquial. It may not be a good translation though, as it clarifies that they are also snakes rather than something else. I suspect the Hungarian does not do this . . .
Animals are usually "foltos": salamanders, cows, some cats... So foltos means uneven spots that is more likely to happen in nature. If a dress is foltos, it has some stains on it.
Pöttyös: a ball, a dress, a mug... In case of a pöttyös dress, think of polka dots. So here we have more regular, organized, man-made dots.