Sorry for lack of docs, but I didn't manage enough time to describe it well.
Rule is simply - path to file that you want to overwrite have to be same as path to overwriting file after removing "i18n/[lang_code]/" from it.
So if you want to overwrite `vendor/snowdog/theme-blank-sass/Magento_Catalog/styles/_module.scss` for `pl_PL` lang you can use one of this paths:
vendor/snowdog/theme-blank-sass/i18n/pl_PL/Magento_Catalog/styles/_module.scss
vendor/snowdog/theme-blank-sass/Magento_Catalog/i18n/pl_PL/styles/_module.scss
vendor/snowdog/theme-blank-sass/Magento_Catalog/styles/i18n/pl_PL/_module.scss
First option is Magento default, second is best for me (I'm looking into module and see what is overwritten without jumping around project) and third exist, just b/c fits the same rule.