The message 'cx-entrypoint-dialog-page-doesnt-exist-yet' is building its sentence with an autonym, but this is the name of the language in its own language. This will be a mixed of language in a sentence, which makes it harder to read.

Please use the localized language name from cldr extension.

An example for 'de': The sentence

This page does not exist in Deutsch yet. Do you want to create it?

should by

This page does not exist in German yet. Do you want to create it?

In php this is by calling Language::fetchLanguageName( $targetLanguage, $userLang ), but javascript module jquery.uls.data seems missing this information at the moment