There are two ways to localize your blog content:
Option 1: If only some of your posts require a translated version, it's best to use "Tags" to set the localization for each post (i.e. 'en' for English or 'es' for Spanish or 'jp' for Japanese, etc). You can filter your posts based on this tag when calling the API. Here's more on how to do that: https://buttercms.com/docs/api/#tags
Option 2: If each blog posts will require a translated copy for each language on your website, you will need to create a "Blog Post" Page Type and utilize the localization support provided for Pages. Here is more information about Localization for your Pages and Collections: https://buttercms.com/docs/api-client/other#OverviewLocales