If you want to explore the menu manually, look for these characters: Settings/Setup: 設定 (Settei) System Settings: システム設定 (Shisutemu Settei) 言語 (Gengo)
The Linguistic Labyrinth: A Deep Dive into the Pioneer Carrozzeria AVIC-RZ33 and the Quest for English
There is typically no internal setting to toggle the interface from Japanese to English.
Even if you could hypothetically brute-force an English menu, you must understand what hardware becomes useless: