On macOS, it's

    say "enter text here"

To pick a different voice:

    say -v Fred "enter text here"

To list voices:

    say -v "?"

(The quoting is necessary to prevent ZSH from interpreting the question mark as a glob.)

I hear Firefox's TTL is important, yet prior to your comment I didn't even know it existed. This sort of stuff should be more discoverable, and have a more accessible (ahem) API.