I have created following store structure;
Website: xxx.de
Store: Germany
Store View: German
Website: xxx.nl
Store: Netherlands
Store View: Dutch
Website: xxx.fr
Store: France
Store View: French
I want to use all languages on other websites too like French and German on xxx.nl with Dutch language. I don't want to create same languages under stores it's to much work for translation and i do use "Add Store Code to Urls" option i will keep it too for all websites.
To configure a multi language website -
1. create a new store view
2. set locale by going to Admin Panel > Stores > Configuration > Store View > [Store View Name].
3. In General section find Locale Options and set a language for the store view and save the configuration.
For Reference - https://magefan.com/blog/configure-magento-2-multi-language-store