There's a few DECtalk projects on Github (main, but there's other repos too) that people seem to be working on, including one for the game engine Godot. That one seems to have some problems (need to move files, broken OotB for me, broken dictionary after all that), but I was able to make a script (see my comment here) to properly call+play it.
They have plaintalk too and that's what I was initially interested in, was trying to get it through WASM (for multi-platform) but even after the above I'm still lost.