Code:
public Form1()
{
dataGridView1.CellFormatting += new DataGridViewCellFormattingEventHandler(dataGridView1_CellFormatting);
}
private void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
if(e.Value != null && e.Value.GetType() == typeof(bool))
e.Value = ((bool)e.Value ? "da" : "ne");
}