The pronoun for "many a language"

Could you please tell me which sentence is correct?

1. It's not worth learning many a language when you haven't got the
   opportunity to use them.


2. It's not worth learning many a language when you haven't got the
   opportunity to use it.

Until now, I've only known that "many a + singular noun" takes a singular verb. Unfortunately, I've never heard about the correct pronoun for it.

Before I posted this question, I'd done some searching and this is the only one that I've found useful. But it seems to be a mere opinion, not an officially accepted usage or something like that. What I really want is a widely accepted usage.

Please enlighten me. Thanks in advance.

P/s: This is not a duplicate of this question. In other words, I've already known the use of "many" vs "many a". You can clearly see that my question isn't about "many" vs "many a". In addition to that, the link above refers to a question that doesn't even mention anything about "pronoun" while mine is mainly about it.

Answer

Neither of those sounds correct to me. Many a is a rather unusual construction: as you know, it takes a singular verb because each individual of the "many" acts or is acted on one at a time. However, when referring back to the many whatevers, we ordinarily use another "group of individuals" structure: either them all or each one rather than a simple they or it.

Some examples of what I mean:

Since those days I have had many a good dog at my side and many a good time beside them, and I have loved them all . . . . (A. Hunter Smith, A Life Afield, 2014)

Many a heart is aching, if you could read them all (Charles K. Harris, "After the Ball", 1891)

I've been to many a dentist and each one has been a exercise in some kind of torture. (Scott McIntyre, Facebook dentist review, 2016)

How many a year has passed and gone
Many a gamble has been lost and won
And many a road taken by many a first friend
And each one I've never seen again.
(Bob Dylan, "Bob Dylan's Dream", 1963)

So for your example, you would need either

It's not worth learning many a language when you haven't got the opportunity to use them all.

or

It's not worth learning many a language when you haven't got the opportunity to use each one.

Also, I will point out that (as these examples demonstrate) many a is a fairly poetical/literary phrase, and isn't very common in regular conversation. Use it mainly when you want to evoke a more lyrical feeling.