What do you mean by “from scratch”? Say you have an encoder-decoder model, you have to give the decoder something to generate the text output. The only thing I see would be that you sample a random vector from your hidden/latent space, give it to the decoder and hope for the best. I tried that a bit with a Variational Autoencoder for sentences, and the results are questionable at best (but I cannot exclude that I made mistakes)