Este strategy for i18n (multiple languages)
Server detects user agent locale and returns internationalized app, if possible. Server doesn’t redirect.
With this approach, the same URL provides different content. It means, example.com/about will render both English or Czech content. I believe it’s ok because server also provides language annotations for crawlers.
Therefore, cs.example.com/about will work as expected. Both for the user and the crawler.
What about links? The same. Link from example.com/about will go to example.com/blog, while link from cs.example.com/about will go to to cs.example.com/about.