[sisˈtɛm ɛ̃tɛʁnasjɔˈnal]
Here's a breakdown:
* Sys: Pronounced like "siss"
* tème: Pronounced like "tem"
* Inter: Pronounced like "in-ter" (with a slight emphasis on the "in")
* national: Pronounced like "na-syo-nal"
Remember, the "e" at the end of "Système" is silent.
Important Note: In French, the stress is usually on the last syllable of a word.