I havenât seen a website like this, but I also think that this would be really hard to create. Taking an English sentence and then translating it to native Japanese would be, well would just be learning how to translate from English to Japanese. I donât think this would be a good way to practice your ability to build sentences (output) because it forces you to go from English to Japanese, rather than just thinking of it naturally without needing to go from English to Japanese. I can see this working with simpler sentences, but as sentences get more complex I donât think this would work very well, which makes me think that there probably isnât any website that does this.
Edit: Now that I think about it you can actually do this (kind of) without the need of any specialized website. Find a show with English subs, mute it, and then look at the subs and try and figure out what the person is going to say in Japanese. I think this is probably as close as youâre gonna get to something like this, but once again this is just practicing how to translate rather than âsentence buildingâ.