There is no online demo but you can run the pre-trained models on your local machine: https://github.com/facebookresearch/fairseq#quick-start. CPU-only versions of the models are available as well.

For a comparison with other translation services, keep in mind that our models have been trained on publicly available news data exclusively, e.g. this corpus for English-French: http://statmt.org/wmt14/translation-task.html#Download .