Welcome to the WPML support forum. I tried to visit your site but it's "under construction".
So here are few things you can check on your end:
- Go to "WPML > Languages > Language URL format" and resave your choice (Different languages in directories).
- On the same page, section "Hide languages": did you hide this language? If so, go to your profile and activate the option "Display hidden languages".
- Go to "Settings > Permalinks" and resave your permalinks
- Access your server via FTP (or Cpanel) and make sure that you don't have a /cs folder (if you have one, delete it - WPML take care of the language repertory)
- Still using FTP, check if you have specific directives in .htaccess that would create that issue. An easy way to discard this issue is to rename the file (.htaccess_old) and resave your permalinks. That should create a new .htaccess
- It could be a compatibility issue with another plugin. Can you try WPML in a miminal environnement?
1. Disable any additional plugin that is not related to WPML and its add-ons and switch to a default theme like 2020.
2. If the issue disappears please start reactivating the plugins one by one, or activate them in small groups. This way you can verify at which point the issue appears again and identify the plugin that is causing the issue.
Please also enable WP_DEBUG to see if you have any PHP errors.
