May I know which version are you using? As far as I know, from verson 2016 and above, multi language support is enhanced. Also if post some screenshots, it will help better understand this issue.
We're running version 7.7.3
Below image shows the history as correct yet the Actions as incorrect (Bijlage toevoegen is incorrect - it should be shown as per the history as opdracht toevoegen) Bijlage toevoegen when clicked on is Add Assignment.
Below image shows that the business object for Add Assignment has been amended (no idea where it's pulling Bijlage toevoegen from)
Had to be done via the process In-Progress action - updated the attributes here with the correct information and worked fine.