Instead of adding your language pack to vendor directory - add language pack to app/i18n directory.
Below is the detailed instructions step to install Bulgarian(bg_BG) language.
- Download the Bulgarian (bg_BG) language pack from this link - https://github.com/denchev/magento2-bulgarian-language-pack
- Create app/i18n/denchdev/bg_bg/ directory and put all the downloaded language-pack files in this bg_bg directory.
- Now Upgrade installation using command - php bin/magento setup:upgrade
- Clear cache using command - php bin/magento cache:clean
- Deploy static content command - php bin/magento setup:static-content:deploy bg_BG
- Now to activate the language for frontend , logged in to admin panel then go to stores -> configuration -> general settings -> locale options -> select Bulgarian language from locale dropdown - Also Make sure you have selected store view from storeview dropdown on the top of the settings screen.
- Click on save buttton and check on frontend side content will shows in bulgarian language.
For More Details refer this link - https://github.com/denchev/magento2-bulgarian-language-pack
Note : While doing this all make sure you are in developer mode - as magento 2.2.2 version you can not change locale while your in production mode.
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