Recently we faced a strange issue with translations. It was showing correct translated value in the Form, however the same field in the Header was showing the label in English instead of German.
In Development environment it was working properly only in TEST we were facing this issue after deployment.
Then just to give it a try, I opened the form for customization, removed the City field form Header and added it back and did publish.
Surprisingly it started showing correct translated label in the header.
Hope it helps..