Learning Japanese has been some of the most difficult "schoolwork" of my life, and I indulged myself in a long stint in academia! Three (!) character sets to learn, very different structure, much more contextual than English (or Spanish), etc. And actual day-to-day spoken and written Japanese can be pretty different from "textbook" Japanese, even the more-formal "keigo" forms you use with strangers, work superiors, etc. If you mostly study to pass a JLPT (Japanese Language Proficiency Test) level, your Japanese will sound a bit stilted to a native speaker. They'll still heap praise on you for trying,* but they'll know how you learned.

Japanese is better than English at actually following its own rules (what language isn't? lol), so that helps...but it's been a challenge.

* It's a running joke among foreigners in Japan that you constantly hear "日本語 上手" ("your Japanese is good") right up until the point that it actually is good...after which you will never hear another word of praise. ;P