By the way, the spell checker works just fine in MS Word 2010.

Looking around on the Internet, I found that in the case of Microsoft Office 2010 (the version I am using), the dll is Microsoft.Office.Interop.Word, Version=14, whereas Trados Studio looks for Version=15. This is likely why it cannot find Microsoft.Office.Interop.Word, Version=15.0.0.0. If that is the case, is there a simple workaround, or do I need to switch to a more recent version of Microsoft Office? In the latter case, which versions of Microsoft Office are supported?

Problem solved! As I surmised, the issue appears to be that Trados Studio looks for a DLL of a different version than that of Microsoft Office 2010 (Microsoft.Office.Interop.Word, Version=14). Replacing Office 10 with Office 2021 (Microsoft.Office.Interop.Word, Version=15) took care of the problem and I was able to switch to the Microsoft spell checker.

Hello.... Any idea if I use the latest version of MS Word? I have a Microsoft 365 subscription... I would expect that Trados Studio be able to use the latest versions of the DLLs.

I will appreciate any ideas.

Hello.... Any idea if I use the latest version of MS Word? I have a Microsoft 365 subscription... I would expect that Trados Studio be able to use the latest versions of the DLLs.

I will appreciate any ideas.