Question

How can I do this more efficiently? Ideally so I can call showTag without any arguments and it returns the correct comboBox.

I added the argument table to define whether the value returned by showTag was from comboBox1 or comboBox2. So if i want the value for comboBox1 I call showTag(1), if I want the value for comboBox2 I call showTag(2)

//Return the currently selected language
public string showTag(int table)
{
    string LanguageSelection = String.Empty;
    if (table == 1)
    {
        LanguageSelection = comboBox1.SelectedItem.ToString();
    }
    else
    {
        LanguageSelection = comboBox2.SelectedItem.ToString();
    }
    string[] LanguageTag = LanguageSelection.Split(' ');
    string tag = LanguageTag[1].Replace("<", "").Replace(">", "");
    return tag;
}

Answer 1

you have to add a SelectedIndexChanged event on the same function for your 2 combobox (go to properties of your two combobox and click event and SelectedIndexChanged)

private void ComboBox_SelectedIndexChanged(object sender, System.EventArgs e)
{
            ComboBox cb =  (ComboBox )sender ;
            LanguageSelection = cb.SelectedItem.ToString();
            string[] LanguageTag = LanguageSelection.Split(' ');
            //string tag have to be declared in your application at a global level
            tag = LanguageTag[1].Replace("<", "").Replace(">", "");

}