For multilingual websites, each page must be duplicated and translated. The file name in the language other than the main language must have the format <file name>.<language code>.md.
For example, this page is written as a file named multilang_posts.md. Suppose the main language of the website is English and there is also a Japanese version. In order to create a Japanese version of this page, you need to create a file named multilang_posts.ja.md and translate the contents.
Check Going global or the official Hugo documentation on how to set your website multilingual.
