According to C-canon, Liliac (and Jabba) spoke Basic.
Han bowed again. “Lord Jiliac,” he said, in Basic, “it is a privilege to meet you, Your Excellency. Your cousin Lord Tagta says that you are always in need of good pilots.”
“Pilot Solo”-Jiliac turned bulbous eyes layered in fat upon Han, and peered down at him with faint curiosity-
“do you speak and understand Huttese?” (Clearly, he spoke in Basic as he didn't know if Han understood Huttese)
“I understand it, Your Excellency. I do not speak it well enough to convey the beauty of the language, therefore it is not proper for me to attempt to utter it,” Han said earnestly.
...
Han bowed to the younger Hutt. “Greetings, Your Excellency.”
“Greetings, Captain Solo,” Jabba replied with a gracious wave of his small hand. “Your reputation precedes you.”
Jiliac held out his own hand. “Enough chitchat. The holocube, Captain?” “Certainly, Your Excellency.” Han produced it, handed it to Jiliac.
(src: Han Solo series Book 2 - The Hutt Gambit)
Please note that if you search for "Huttese" in book, you will see that it's very frequently mentioned that Hutts speak in Huttese specifically in various situations (including to Boba Fett). Therefore, the lack of such clarification here makes me assume it was Basic.