I've set up multi-store view with multi language, but I'm facing a weird issue that is default store view is running perfectly but another store view is not able to load CSS.
First you need to check the network tab in developer tools you'll need to see what are the files missing'404'
I think you'll need to deploy statics considering the languages/locales you use in these store views
ex. you've locales
for deploying statics you should use the command
php bin/magento setup:static-content:deploy en_GB es_ES