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 = 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