What adds the parameter to the URL?
Sounded like this parameter gets added on it’s own, but I don’t think this is something that would happen.
I’m actually playing with the idea of duplicating my pages to translate right now. As long as hreflang and canonical tags are set right, nothing should go wrong with SEO.
As a matter of fact, hreflang tags are good for SEO because the URLs in the cluster share their ranks, so it helps other languages that have a lower score to rank higher.
An other point to consider is using folders to classify the different languages.
You would then get something like https://www.example.com/name-of-page for the English variant and https://www.example.com/es/name-of-page for a Spanish variant.
As far as I know, google takes URL structure into consideration to localize websites (someone can correct me on this if I’m mistaken).
This also makes it a little more tidy to work, so can’t really hurt.