Learn Polish: Chcę przestać przeklinać w pracy. - I want to stop swearing at work.

Verbs of cessation like przestać (to stop) must always be followed by an imperfective infinitive. This is because you can only stop an action that is ongoing, continuous, or habitual. You cannot logically "stop" a one-time, completed perfective action!

Why did we use the perfective przestać instead of the imperfective przestawać?

You are expressing a desire to accomplish the act of stopping once and for all. The perfective przestać focuses on that completed result. If you used the imperfective przestawać, it would mean you want to be in the ongoing, gradual process of stopping, which sounds very unnatural for this specific sentence.

Is it normal in Polish to have two infinitives in a row like przestać przeklinać?

Yes, this is a standard verb chain. The only conjugated verb is the first one, chcę (I want). Because "wanting" leads to an action, it takes the infinitive przestać (to stop). Then, because you have to specify what you are stopping, przestać takes the next infinitive, przeklinać (to swear). Unlike English, which switches to an -ing word (swearing), Polish just keeps linking infinitives.

Just as a refresher, why does praca (work) change to pracy here?