Add pronunciation to text to speech
Yes, you can affect macOS's text to speech pronunciation. Everything you need to know is in Apple's Speech Synthesis in OS X.

Try these two commands in Terminal.app:

say "cat"


Now to have the individual letters spelt out:

say "[[char LTRL]] cat [[char NORM]]"


See Use Embedded Speech Commands to Fine-Tune Spoken Output for a long list of modifiers.

If you need to speak in another language, be sure to use an appropriate voice.