Chains are made of a lot of oval shaped units. What is each one of them called in English?
I don't know the name in my native language either.
It's called a link. From Wikipedia,
A chain is a series of connected links which are typically made of metal. A chain may consist of two or more links.
I believe you could also use "ring".
P.S.: I should add from the Cambridge dictionary, that a chain is "a set of connected things". In particular, look at the second definition: "(a length of) rings". The word "link" never appears on the page, even though I can agree with the @Max's definition.
Almost the same is stated in the Oxford dictionary - chain:
[countable, uncountable] a series of connected metal rings, used for pulling or fastening things; a length of chain used for a particular purpose