The day that you bring your daughter home for the first time, everyone is very emotional and tired after all of the legal processes and long flights. You are so relieved and so full of joy to be home with her though. Your little girl does not speak English yet and you try hard to communicate with her and to make her feel at home. When you show her to her bedroom she is greeted by your dog. She reaches down to pet the dog and speaks to him in Japanese, then to her utter delight and surprise the dog responds to her words by sitting down. She gives the dog a couple of other commands and watches with joy as he responds to those as well, instantly making her feel understood and more at home. The night that you found out that you would be bringing her home you both decided to train the dog in Japanese instead of English, and you are so thankful now that you did.
There are many wonderful reasons to teach a dog to respond to Japanese commands. Perhaps someone you love speaks Japanese and you wish to train the dog for his sake. Perhaps you speak Japanese so you would like for your buddy to understand Japanese. Perhaps you will be moving to Japan with your dog. Perhaps you just like the Japanese language and prefer that your dog responds to Japanese commands instead of commands in another language, or perhaps you would like for your dog not to respond to anyone other than yourself. Whatever the reason is, you can learn how to teach him what he needs to know.
Which method will work best for you will depend mostly on what your dog already knows. If your dog has already been taught commands in another language, then the 'Command Replacement' method will probably be the easiest method to use to teach him. If your dog already knows hand signals, with or without commands in a language other than Japanese, then the 'Hand Signal' method should work best. If your dog has never been taught the behavior that you would like to train or if you would simply like to start from scratch either way, then the 'New Command' method will be the best method for you to use.
If you are using the 'New Command' method, then you will need a resource for teaching specific commands, that is written or spoken in a language that you understand. Wag! Walking's Training Resources Page is one such resource. It includes articles, such as this one, with instructions for training certain commands, with several different methods to choose from in each article. These articles can be used to teach the specific commands that you choose to teach, and then adapted for the Japanese commands by following the steps in the 'New Command' method.