I don't think a native English speaker would EVER say "There is money in this pant." (offered as an alternate).
Not in America, for sure.
Not in England either. Also, we wouldn't say "There is money in these pants", we would say "There is money in these trousers". We would not say "There is money in this trouser" either, which I would guess is the equivalent translation.
Agreed. The alternate translation conjures up all kinds of images:) Perhaps a police investigator would hold up a piece of evidence and declare: "There is money in this pant!"
In English, trousers/pants is always plural: "un pantalón" = one piece of clothing for one person's legs = [one pair of] trousers(UK)/pants(US). "dos pantalones" = two pieces of clothing = two [pairs of] trousers/pants. The only case when it's singular is "one trouser leg". One pair of trousers is made out of two trouser legs (and some more fabric to hold it together).
So if you see "trousers"(UK) or "pants"(US) and you want to translate it into Spanish, you have to discern from context whether it's "pantalón" or "pantalones". Whereas from Spanish to English, it's always going to be pants. Or trousers. (Be mindful in which part of the world you are; hilarity might ensue;))