Special action required for one item in a listbox

Can anybody please help with the folowing request,

To add an item "other" to the array (the easy bit) and when a user selects this item, an input box pops up and allows the use to type in text and then for it to get listed in the same cell location. Many thanks for any assistance.

Option Explicit

Private Sub CommandButton1_Click()
Dim i As Integer
Dim s As String
'ActiveDocument.ListBox1.Clear
s = ""
For i = 0 To Me.ListBox1.ListCount - 1
If Me.ListBox1.Selected(i) = True Then
s = s & Me.ListBox1.List(i) & ", "
End If
Next i
'
If Len(s) > 0 Then
s = Mid(s, 1, Len(s) - 2)
ActiveDocument.Unprotect
ActiveDocument.Tables(1).Cell(9, 2).Range.InsertAfter (s)
ActiveDocument.Protect (wdAllowOnlyFormFields)
Else
ClearCell
End If

Unload Me
End Sub

Private Sub CommandButton2_Click()
ClearCell
End Sub

Private Sub UserForm_Initialize()
Dim vArray As Variant

vArray = Array("cs", "da", "de", "et", "el", "en", "es", "fr", "it", "lv", "lt", "hu", "mt", "nl", "pl", "pt", "sk", "sl", "fi", "sv", "other")
Me.ListBox1.List = vArray

End Sub

Private Function ClearCell()
ActiveDocument.Unprotect
ActiveDocument.Tables(1).Cell(9, 2).Range.Delete
ActiveDocument.Protect (wdAllowOnlyFormFields)
End Function