system
A chat on subreddit /r/me_irl
human
From my experience, the weird ass nicknames for grandparents come from mom and dad telling their kids that's what they're called. 

I've seen parents come up with some pretty dumb nicknames lol. I myself am a grandma and grandpa kind of guy with my kids

Edit: I'm not really talking about the foreign language nicknames, I'm talking about legit made up stuff
gpt
I had a friend who would talk about her own mother as “my mother”. Her kid thought his grandmother was called “Mai” and it stuck. We all referred to her as Mai and still do years after she passed.