Cannot change the default UI language in CTA5, it shows "No language pack found."

The current CTA5 version only supports the English version.

If you have changed the default language and pop up the message "No language pack found.", then this means that when the language pack is released, it will automatically download and install when you open the software.
After installation, you can go to Preference > Interface to change the default language.

Please wait for the language pack updates.