For single-language installations (common in educational labs provided by Festo Didactic), you can force a language change by modifying the shortcut properties. This works for FluidSIM 4, 5, and 6.
Overall Verdict: Simple, quick, but limited language options. No in-software language switcher while editing a project. Festo Fluidsim Change Language
If the language option is greyed out or missing from the menu, it often means the software was installed with only one language pack. FluidSIM installers are often region-specific. and 6. Overall Verdict: Simple