"Practise, practise, practise."
Translation:לתרגל, לתרגל, לתרגל.
No, it's actually a regional difference. Americans spell both the noun and the verb as "practice," while Brits use "practise" for both meanings.
It's the correct spelling of the verb. Compare with advice and advise. The one with s is the verb.
I don't understand this translation - why is it the infinitive? An imperative sounds better, maybe? (In British English, "Practise, practise, practise" would be three imperatives; "Practice, practice, practice" would be three nouns.)