You have to get custom firmware on your 3ds to bypass region lock to be able to play US games. To make the 3ds entirely English from Japanese, you have
to preform a region change from JP to US. All info needed to preform this can be found on this site https://3ds.guide/
If you happen to have a copy of cubic ninja or a copy of freakyforms deluxe, you could launch regionfree that way. Otherwise, buying a $20 flashcart from nds-card.com will allow you to install a cfw (custom firmware). 3ds.guide should go more in depth about this.