I wanted to know how to modify this to handle localization to Japanese version.
Hi @raginimishra123, in the future, make sure you refrain from posting your api key here since this is a public forum! You may want to deactivate your key and create a new one since others may have seen this post.
The Single Send API does not support multi-language content. You should create separate transactional emails in each different language and send the proper email to each contact based on their location.