PowerPoint: Change Presentation or Selected Slides Language

I have updated my previous VBA based solution to change a language in PowerPoint: now you can change the language of the whole presentation or of selected slides only. In some cases you may have some slides in a different language e.g. English instead of presentation language in German.

PowerPoint: Change Language in whole Presentation (VBA Macro)

See updated version.
Working in an international environment, I need a lot of time to fix the language in a whole PowerPoint presentation. There is no built-in feature for this available. I share here my VBA based solution.