You can add a function in your template like this:

 <xmod:Template runat="server" .............>

<script runat="server" language="vb">

    Private Function Add2Head(sIn As String) as String

            'Get the head element
            Dim oHead As HtmlGenericControl = Me.Page.FindControl("Head")

            'Create literal and parse the tokens
            Dim litAdd As New Literal
            litAdd.Text = String.Format("<meta rel='alternate' hreflang='{0}' />", sIn)
            

            'Test if head exists
            If Not oHead Is Nothing Then
                'Inject the string
                oHead.Controls.AddAt(0, litAdd)

            End If

            Return "Write Meta"

        End Function
        
</script>

Then you can call this function inside your item template:

  <ItemTemplate>
    <%# Add2Head(Eval("Values")("TabId"))%>

You need code to prevent the meta tag from being injected for every item, but you sould simply add a varialbe for that.
I did not manage to call this from the header or footer template with the databinding.