Dear Ann,
Thank you for your letter! I was very interested to hear about your decision to learn Japanese. I also think Japanese cartoons are cool!
To answer your questions: At school, I learn English and German. I would really like to learn Spanish because I think it sounds beautiful and it would be useful for traveling in South America. I think your choice of Japanese is great! If you're passionate about it, that's the best reason to learn a language. Don't worry about it being hard; if you enjoy it, you'll be motivated to keep going.
Write back soon!
Best wishes,
[Your Name]