I like the idea of creating tutorials (or translation databases) to help people learn Japanese (or any other language) solely because I believe it is a good thing by itself. That is, I am not particularly concerned about how such tutorials would impact the quality of scanlations. I simply think that having the tutorials is better than not having them.
I assume most of those working with scanlation are young people learning the craft and that not all of them are aiming to actually translate manga as a profession. Who am I to judge the reason for young people's hearts? Whichever the reason may be, what we get in the end is not the fruit of years of polishing their skills, it is the result of their process of
learning it by doing it -- something like learning a language as
praxis. In that sense, I expect to see mistakes. Lots of them. But I also expect that some of them, not all, are willing to take edifying criticism (because some criticism is done just to put people down) and improve themselves.
I think it is valid to help those who are trying to improve. And if by helping those who want to learn you end up also helping those not really concerned about learning, then all the better.
You see, translating is hard. I think it is valid for an author to use "うそ" as the interjection "no way", but meaning "lie" because the theme of his text is "lies". I can't obviously think of any real-life example other than José Saramago's prohibition of translating his book "
Ensaio Sobre a Cegueira" (Blindness) from Portugal's Portuguese to Brazilian Portuguese because he wanted the words as they were to not change their meaning. As you start delving into
etymology, you start seeing that synonyms are only valid in casual speech. Certainly, I doubt this would be the case on scanlation, but it is just a thought on the complexity of the issue.
Anyhow, back to the matter at hand, I believe the easiest way to test your idea of creating tutorials is to use
Wiktionary. They already have a system that allows users to enter the definition of words and even have discussions on how to define them. You would need to check how the system works and you can even start a discussion there on how scanlation issues could be addressed there. Although Wikitionary's purpose is not to help scanlation, it should still be interested in improving the quality of its word database. And if you give up on the tutorials, your work will be part of a larger project that will continue to use and improve on it.
So I think it's a good idea that can be quickly prototyped with existing tools. I understand that as a "business", Mangadex would benefit from having its own dictionary. But even so, I think I would stick with Wiktionary because I think that no one "owns" the language and WikiMedia has proved as a trustworthy company in the sense of making knowledge freely available.
Best of luck! =)