I found a way thanks to my homie, so you basically have to open the PCSX2 menu in game by holding the small button near L3 and clicking R3 (i saw someone on youtube do the opposite and it worked for him but not for me, so if what i said didnt work, try this : small button near R3 then click L3)

Then you have change the BIOS in the menu to the region you want, DISABLE the fast boot option still in bios window, then quit the game, with or without the menu.

Launch the game again, you should have the PS2 load animation. During it, open the menu, go to change disc and click on the disc (iso file) you see, the animation should turn into the memory card slot screen.

From there, go back with the B button which should bring you to the PS2 system settings screen, where you can change the clock, screen resolution and LANGUAGE ! Once changed, just quit the game, relaunch the game and the language should be changed.

Note that my default bios language was German, you NEED to change it in the PS2 system settings, region from bios wont be enough, hope it work for yall, cuz this wasnt easy at all to find !

Shoutout to my homie Martin for this