I think the audience that would be interested in this is vanishingly small, there exist relatively few conversations online that would be meaningfully improved by this.
I also suspect that automatically translating a forum would tend to attract a far worse ratio of high-effort to low-effort contributions than simply accepting posts in a specific language. For example, I'd expect programmers who don't speak any english to have on average a far lower skill level than those who know at least basic english.
It should be an intentional place you choose, and probably niche, not generic in topic like Reddit.
I'm also open to the thought that it's a terrible idea.