Elvenlabs is currently the best but you can get some very good results with first xtts then rvc as a second pass. It involves fine tuning models and running things with python and notebooks, so requires some know how.
The language adds an other layer of difficulty, I would try their demo first to see if it gives anything workable but it isn't a language current tts software cater too, it doesn't seem to be an available option on xtts sadly.
Thank you for the tips. As I see it currently, I expect the language to be the biggest hurdle. It doesn't appear like something I can add myself, even if I had the data for a model. So as far as I can tell it involves two currently more or less impossible steps: Get model data and teach language to model.
If you have material with him speaking in English, you might be able to train an xtts model on it and then use that to bypass the elvenlabs captcha but I'm not sure if they give enough time. Although GPU rental is cheap these days, so captcha time is less of a factor.
If anything, the tech is moving quite fast, it will definitely be easier in a few years, maybe even months.