From Halopedia, the Halo wiki
The language spoken by the Kig-Yar seems to consist of a range of hisses, growls, screeches, snarls, and squawks, though it is intelligible to other members of the Covenant. The Kig-Yar written language was similar to Sangheili, with symbols representing words.
The Kig-Yar are capable of speaking Sangheili, which serves as the lingua franca to the Covenant. In addition, Kig-Yar are also capable of speaking the human English language in a rasped manner. However, most Kig-Yar are unable to form a proper "f" sound in speech. After the Human-Covenant War, some Kig-Yar often spoke amongst each other in odd mixes of English, Sangheili, and the Kig-Yar dialect. During the last days of Jul 'Mdama's Covenant, Kig-Yar mercenaries would often disregard their leader's order not to speak heretical languages, and would often taunt human and Swords of Sanghelios enemies in English.
Known words of the Kig-Yar language include:
List of appearances