While it is easy to change the proofing language for selected text containers, doing so one text container at a time can be a great time-waster, especially if you need the language changed across all content in many slides. There are three ways to set the proofing language for your entire presentation, and you can use one or more of these approaches. Make sure you have the proofing tools installed for all or any of the languages that you need to work within PowerPoint.
Learn how to set proofing language for an entire presentation in PowerPoint 365 for Windows.