Some languages don't work when using Word 2007 Spellcheck from Interop

I'm using the Word 2007 spellchecker via Interop in a VB.net desktop app. When using the default language (English), it works fine. If I set the language to French via LanguageId, it also works. But if I set it to French (Canadian) (Word.WdLanguageID.wdFrenchCanadian), it doesn't work. There's no error message, it simply runs and says the document contains no errors.

I know it does, if I paste the exact same text into Word itself and run it with the French (Canadian) dictionary, it finds errors. Just why that dictionary doesn't work is kind of a mystery to me.

Full code below:

Public Shared Function SpellCheck(ByVal text As String, ByVal checkGrammar As Boolean) As String
    ' If there is no data to spell check, then exit sub here.
    If text.Length = 0 Then
        Return text
    End If

    Dim objWord As Word.Application
    Dim objTempDoc As Word.Document
    ' Declare an IDataObject to hold the data returned from the 
    ' clipboard.
    Dim iData As IDataObject

    objWord = New Word.Application()
    objTempDoc = objWord.Documents.Add
    objWord.Visible = 开发者_如何学运维False

    ' Position Word off the screen...this keeps Word invisible 
    ' throughout.
    objWord.WindowState = 0
    objWord.Top = -3000
    ' Copy the contents of the textbox to the clipboard
    Clipboard.SetDataObject(text)
    ' With the temporary document, perform either a spell check or a 
    ' complete
    ' grammar check, based on user selection.
    With objTempDoc
        .Content.Paste()
        .Activate()
        .Content.LanguageID = Word.WdLanguageID.wdFrenchCanadian
        If checkGrammar Then
            .CheckGrammar()
        Else
            .CheckSpelling()
        End If
        ' After user has made changes, use the clipboard to
        ' transfer the contents back to the text box
        .Content.Copy()
        iData = Clipboard.GetDataObject
        If iData.GetDataPresent(DataFormats.Text) Then
            text = CType(iData.GetData(DataFormats.Text), _
                String)
        End If
        .Saved = True
        .Close()
    End With
    objWord.Quit()
    Return text

End Function

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Are the languages which don't work actually installed for the spellchecker?

And if you try to change the language to for example German? (or Italian but not Italian (Switzerland))