Martin, it's been about a million years since I took French in school, but am I correct in remembering that in French you have serie singular and series plural? In English, the singular and plural are the same: series. My dictionary (which isn't the best) is a little fuzzy on exactly why that is.
Indeed, we say : "Une série", "Des séries".
So basically, one is the plural form of the other.
In French, if you have a group of things, it is usually singular.
That why we have an extra pronom. You have :
In French, It doesn't exist, because objects are referred to as He/She depending on the object ( Série, for example is feminine ).
But, at the 3rd person of the singular, we have On, which is kind of a "impersonal" pronom.
You might say : "Somebody knocks on the door".
In French : "On cogne à la porte".
"On" could be She, He, It, They, etc... but it is singular because they are doing the action together.
However, in Québec ( as opposed as to in France ) On also means groups, such as : "Do we go ?" should be "Est-ce que NOUS y allons" ( 1st person plural ) but we often use "Est-ce qu'ON y vas ?" ( 3rd person singular ).
But it is not strict French...