Clubfox
Perhaps the template you edited and the template that your using are two different templates. Certainly I would expect your Normal to be a Normal.dotm not a dotx. And then different styles can have different languages applied to them so you have to check every paragraph style. And then you need to ensure there isn't any local language overrides applied to the text. And then you need to pay attention if you paste in content from other documents which contain other language-tagged content.
But if you get your template right and use it properly, you shouldn't encounter problems very often, nor will you need macros to constantly reset anything.
Here is a macro you can use to ensure the entire document is being checked in Australian. This involves setting EVERY style as well as making sure there is no local language overrides on content already in the document.
Code:
Sub SetLanguage()
'Changes all the styles in the document to Australian spelling
Dim aStyle As Style
For Each aStyle In ActiveDocument.Styles
If aStyle.Type = wdStyleTypeParagraph Then
aStyle.LanguageID = wdEnglishAUS
End If
Next aStyle
ActiveDocument.Range.LanguageID = wdEnglishAUS
End Sub