For the first time, I tried DeepL.
English not being my mother language, I first tried it with English-mother language (based on alphabet) : it was astonishing. I can't say it was perfect, but honestly I was impressed.
I then decided to try it with Japanese (one chapter of a LN to be precise) : and again, I was impressed. The result was far lower in quality than my first attempt, but nonetheless, it was probably the best MTL I've ever seen. Also, note that the chapter I used had only a few dialogues, maybe it would have been a different result with a VN having a lot of them.
Oh, well, but everything I just said is quite well known I guess... then why do I post this ?
It's simple : I just wanted to warn the people that use DeepL, be it for VN or anything else. There's a deep flaw going with it : it is too good in a certain sense.
Too good ? WTH ? Well, DeepL seems to be able to give sense to a sentence most of the time. Yeah, give sense even if the translation fails (partially or completely), and you the reader might not notice because the sentence might even make some sense in the context, just that it has not the sense it is supposed to. While the Google Translation lot would most likely just send you an unintelligible text that would at least warn you of the failure.
I'm not sure there's a workaround, but I guess one should try, if possible, to use at least two engines in parallel and hoping to get the better of them.
Note : my level at reading Japanese is quite high when we are speaking of reading VN/LN/Mangas etc. I'm positive I encounter very few passages I'm not correctly understanding and, when this happens, I generally know enough to get that I missed something, allowing me to do a bit of research if I feel like it. I'm not sure how I would fare with true literature for example (a lot less good I presume, but I guess it would depend of the writing). Also, when possible I'm still using a text hooker to help me seek out the few kanjis or words I might not know or remember.