I am also quite late to the party but I wanted to add a few things in to this. With copyright, in this case, it is a derivative work. So by that, it is in violation of copyright. In the US anyway. But there is several exceptions to the rule. If it is done for personal use. That is allowed within fair use of a product as it is not distributed at all. Also, this can also be skirted if the translation was being done for the individuals practice of the language, thus an educational purpose. Another factor is that it would be up to Manga gamer to prove, upon release of the fan translation, that it posed a threat to their bottom line. If there are no links provided or anything allowing you to obtain the product directly and required a legit copy of the game, that would fall upon them.
Another factor is that if there is a complete translation, and Manga Gamer is dragging their heels, And Aaeru is indeed not concerned about credit of the translation, she can enter into contract with the original creators in regards to the translation specifically as a separate derivative work and either obtain permission or something else depending on the decision of the original creator.
Just a little food for thought.