On the startup screen, look for a language dropdown menu.
If the software is already installed, you can often change the interface language through the internal settings. Festo Fluidsim Change Language
The most direct way to set your preferred language is during the initial setup process. On the startup screen, look for a language dropdown menu
Note that changing the interface language will update menu bars and dialogs, but some custom library components or older circuit labels may require manual renaming. FluidSIM 5 - Version history - Art Systems Software GmbH On the startup screen