For learning new languages, LLMs often default to some specific level of formality that doesn't apply to all scenarios, so using it as an aid might be helpful but it can't wholly replace lessons.
This comes up with Japanese as well apparently. My partner sometimes uses ChatGPT to practice new languages, but it defaults to a more formal form than you'd probably use with friends. Not a huge issue, but just be aware you'll need something else if you want to properly learn and not just practice a little.