Earlier quoted context omitted.
Some grievances were vague. It doesn't follow our translation guidelines. What specific guidelines did it not follow? It doesn't respect current localization for Japanese users, so they were lost. What was not localized? Mozilla's response should not be limited to clarifying these grievances. But it could have been all the staff member who responded could do.
These ones? https://github.com/mozilla-japan/translation/wiki/L10N-Guide... Looking through that wiki there seems to be a lot of things that ML would get wrong.
I'm sure some translators were using ML before it was integrated, and those guidelines are here in particular to tell them about those problems.
Also, ML is now really good to translate between European languages, but Japanese is very different in its structure so ML from English to Japanese is not as good. I'm sure some people who only know English/French/Spanish/German saw that ML is pretty good, and don't realize that for some other language it just doesn't work.