Dim Trad As String
        Dim XMLDoc As New XmlDocument
        Dim node As XmlNode
        'Dim risultato As String
        Dim percorsoFile As String = HttpContext.Current.Server.MapPath("diz_" & Lingua & ".xml")
        XMLDoc.Load(percorsoFile)
        node = XMLDoc.SelectSingleNode("//translation [@name=""" & Termine & """]")

Trad = node.Value

node = XMLDoc.SelectSingleNode("//translation [@name=""" & Termine & """]")

Protected Sub ImageButton1_Click(sender As Object, e As ImageClickEventArgs) Handles ImageButton1.Click
        Dim LNG As String = Session("lingua")
        Dim Traduzione As Traduci = New Traduci("home1", "EN")
        Literal1.Text = Traduzione
    End Sub

Public Function Traduci(Termine As String, Lingua As String) As String
        Dim Trad As String
        Dim XMLDoc As New XmlDocument
        Dim node As XmlNode
        Dim percorsoFile As String = HttpContext.Current.Server.MapPath("diz_" & Lingua & ".xml")
        XMLDoc.Load(percorsoFile)
        node = XMLDoc.SelectSingleNode("//translation [@name=""" & Termine & """]")
        Trad = node.Value
        Return Trad
    End Function

<?xml version="1.0" encoding="iso-8859-1"?>
<lingua>
  <lang name="english">
    <translation name="home01">Welcome in my site</translation>
  </lang>
</lingua>

Errore  1  Impossibile convertire il valore di tipo 'Traduci' in 'String'.

Dim Traduzione As String = New Traduci("home1", "EN")