conditions htaccess. How to write a condition?

Question

htaccess

There was an old scary project with urls that was never CNC. All urls were via GET. Faced a problem that I can not make a normal condition.
Can someone help with an example.
There is a url like: mydomain.com/?reg=23
You need a url like mydomain.com/?locality/23
And if there are two get parameters: mydomain.com/?reg=23&type=10 then there should be a redirect mydomain.com/catalog/23 /10
That's just the second problem.
Moreover, in addition to these, there are get parameters that are not needed at all and must be cut off.