
I recommend that you also modify the language of the Normal style. Try the following code (which is using wdEnglishUS as the language, but you can change that as necessary):
Sub ModifyLanguageCurrentDoc()
'Stefan Blom, MVP, May 2020
ActiveDocument.Styles(wdStyleNormal).LanguageID = wdEnglishUS
ActiveDocument.Content.LanguageID = wdEnglishUS
End Sub