Disclaimer: Long post, but in brief: Iâd discourage continued use of this method. This got away from me as I was writing it, but the longer I thought about it, the worse of an idea it seemed. I really wanted to make my reasons for my opinion clear, so I let it stand.
Anyway.
This can be nice as a sanity check like Sidgr said, and I, myself, did in fact use machine translators when I was just starting out, to check certain words and set-phrases in isolation before I found other, better tools (good dictionaries go a long way). But, by your own admission, using machine translation is an imperfect solution.
This might sound harsh, but Iâd actually go a step further and say that itâs straight-up a bad solution for what youâre trying to use it for, particularly as a learning tool. Donât let Google grade your homework. Itâs like setting yourself up for failure, or at least restricting your opportunity for growth. Grading your successes and failures according to a machine translator will work sometimes, but one tends to learn from their mistakes more than their successes.
What will you learn when you put in a sentence and Google spits out complete garbage? You may have been on the money, but Google (or whatever other service) may not be capable of recognizing when youâve âgot it.â
As a personal anecdote, this happens to me all the time, because I sometimes throw things in there to see how much machine translators have grown since I last checked, and I know what Iâve written is perfectly sensible. Itâs an especially bad problem with casual-register speech patterns.
This is to mention nothing of the fact that itâll be hard for you to organically get a sense for how the all-important background mosaic of Context 
interacts with the language. Subtextual or contextual information missing from the text âproperâ is one of the most famous modes of machine translator failure, and Japanese is notorious for working this way, so if you grade yourself that way, youâll develop a really weird habit of wanting to expressly include all your information textually which would make you come off as unnaturally stiff, or long-winded. Just one example of how this could stunt your growth as you learn.
Bottom line, this sounds like a great way to severely hamper your ability to get a sense for how to put naturalistic/casual sentences together. It might make an oookaaaay stop-gap tool, if only for the most basic of statements, depending on where you are in your learning journey right now, but thatâs the best Iâd ever say about it.
I donât mean to rain or your parade, but I canât really bring myself to just move on from reading this without saying something. You should figure out a better method thatâll work for you without letting yourself settle into getting serious feedback from machine translation. Maybe find someone thatâs either provably fluent in Japanese, or whose abilities you highly trust, to vet the sentences you put together? If you donât already have someone like that, someone in this community might be able to fill the role. In fact, to put my money where my mouth is, Iâll even nominate myself, if you donât have anyone else and want to give that method shot, assuming Iâm of an appropriate skill level to help you out. In fact, maybe a dedicated sentence-vetting thread would even be a good idea.
