In order to translate the CMS block you need to go to Content > Elements > Blocks choose the block you want to translate and press the Add New Block button since the translation of the block requires manual creation of a new one.
CMS Block Info
- First of all make sure you Enable the CMS block.
- Then set the block Title and Identifier. Note that the identifier of the translated block should remain the same as the identifier of the block you are translating from.
- Set the Store View you want this Magento CMS block to be assigned to.
In WYSIWYG editor enter the content of your CMS block and don't forget to press the Save Block button to finish the translation.
CMS Block Translation is just one of the series of articles about How to Configure Multi-Language Magento Website? which include information about the creation of a new store view, language packs installation, useful multi-language store extensions, product&category, email templates, and other translations in Magento 2 website. You should definitely get acquainted with them in order to know how to manage a multilanguage store.