I tried to call it as below but I couldn't. That's why the code is incomplete
private void button4_Click(object sender, EventArgs e)
{
using (ResXResourceSet resxSet = new ResXResourceSet(resxFile))
{
this.Text = resxSet.GetString("buttonError");
}
}

resxSet.GetString("buttonError.Text")-- Are you sure you want to access UI culture related values like this?