Please help to workaround this issue
Translation not working
I'm not fully sure but I remember a project where I found a similar problem, on Magento 2.1.x and I guess after an upgrade there was a solution (or maybe I've ported the fix from 2.2x).
I can't remeber the whole story right now but it was something related with: https://github.com/magento/magento2/issues/8179
Maybe you can try to port the solution and check again.