Make sure that "Detect language automatically" is cleared at Review | Language | Set Proofing Language. This is important, because it prevents Word from changing the language at the insertion point.

To more easily see which language is applied at the insertion point, you can display the language control on the status bar. Right-click the status bar and select the "Language" option on the context menu.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional