Sometimes it is mandatory because there are many games (even from Microsoft) that do not have a language selector and only use the one that the console has, without the possibility of choosing another one unless you change the region. This is especially shocking in the case of Portuguese or Spanish since there may only be translations for another language but by default and poor design of the localization system causes that instead of using the one from another region with the same language, it uses English by default.
And how do you change the language of the games on PC and on xcloud?