I try translate other website. I install language pack via composer. Language pack
pl_PL I found in vendor.
But I research are others folders and I cannot find other languages. eg.
cs_CZ. Any one know how I can find this?
As far as I know there is no official page documenting all language packs, but there is a good compilation of language packs available at Mageplaza (for free, ofcourse) here - https://www.mageplaza.com/kb/magento-2-language-pack/
These can be installed using composer or manually as per your requirements.