Any ideas which ones are the best? I would quite like to use a good open-source api, am happy to pay for my own compute. (I've just used googles before because it was handy. But I wouldn't use it the way telegram have done.)
Huggingface offers a few models that are pre-trained [0], OpenNMT is a good framework [1] as is MarianMT [2]. Many of the best MarianMT models have been ported to HuggingFace.
If you don't want to self host, huggingface offers these APIs at a cost.
[0]: https://huggingface.co/models?pipeline_tag=translation [1]: https://opennmt.net/ [2]: https://marian-nmt.github.io/