Adobe Captivate only comes with a small number of text to speech voices and it seems that everyone gets the same handful of speech agents regardless of installation language. The company Neospeech has been absorbed by the company Readspeaker. They do have the option of purchasing additional languages but they are not easy to work with as they prefer to license their technology differently than how it works in Captivate. One possibility that might work for you if you are on a Windows machine is to install the appropriate language pack that includes text to speech agents. Here is a video where I added Japanese as an example.

https://elearning.adobe.com/2020/03/add-other-text-to-speech-languages-in-adobe-captivate/

Hope this helps

I am not sure to understand your question correctly. You will get NeoSpeech voices fitting with the language of your Captivate application. You can always add other voices and create TTS audio files in the wanted language. If this is not the goal of your question, please clarify.