I work with Loco Translater and have been all near 500 lines several times.
The sentence I would like to get translated is the one that I have pointed out in my first post.
“Please select groups which you want to join.”
which is on the page of Setup / Preferences
Please contact on mail
If after following these 3 steps, still not working, Let me know. I will try to find out alternate way to translate that for you. But before that please follow that 3 steps under “Using Loco Translate Plugin” heading.