In English this is, “hehe”

“Hi hi” would be interpreted as saying hello 2x in quick succession when you are excited to see someone.

We also sometimes use “kk” to mean, “okay, got it.” But emphasized or excited.

Actually, in English it is pronounced the same as in Czech and Polish: /hɛhɛ/ or /hihi/ (as far as I know). Both are written respectively as "hehe" and "hihi" and are valid expressions for denoting laughter in Polish (and as I assume, it works similarly in Czech).