If you want to change the language of CATIA V5-V6 for first time I’m sure that you will try to find the option of change in Option menu, but you will have a surprise. You will not find this option in this menu.
To change the language in CATIA V5-V6 you must navigate to Tools -> Customize and from here to the tab Options -> User interface language where you have the possibility to change the current language to another.
It is possible to not find the language that you want to find, because not all version of CATIA V5-V6 have pre-installed all languages available.
I accidentally changed the language to chinese. Had to call a chinese friend to bring it back to english haha