Hallo,
ich habe die Stellen hervor gehoben, die ich abgeändert habe. Drück dir die Daumen, dass es klappt.
Hello, I would like (klingt einfach höflicher und gerade in Japan ist Höflichkeit ein Muss) to visit Japan in January 2017 and I'm very interested in the opportunity to work as a volunteer at your hostel. I like/love foreign cultures especially Japan.(very interested steht bereits im ersten Satz) I think it's really important and useful to know other people. That's why I decided to do a volunteer service.
For this reason I worked as a volunteer in Afrika two years ago. We built a school and I can say, that this was a very rewarding time for me. You can get an impression of the work done over there through my video on YouTube.
I love to travel and communicate very well with all sorts of people.
I would be very grateful to be part of your team and spend four weeks in your hostel. I am looking forward hearing from you.
Sincerely yours