How to use google translate api or similar for free?

I'm trying to do an exercise for class. It is a translator with JFrame windows. The fact is that I try to use the Google Translate API and it seems to be paid. The error that shows me is the following:

  

[google-api-translate-java] Error retrieving translation.

I have the following code:

private void jButtonEspIngActionPerformed(java.awt.event.ActionEvent evt) {                                              

        try {

        String textoOrig = (String) this.jTextFieldOri.getText();
        String textoTrad;
        textoTrad = Translate.DEFAULT.execute(textoOrig, Language.SPANISH, Language.ENGLISH);
        this.jTextFieldTrad.setText(textoTrad);
    } catch (GoogleAPIException e) {
        System.out.println("Error " + e);

    }
}                                             

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {

    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(Tra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(Tra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(Tra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(Tra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new Tra().setVisible(true);
           GoogleAPI.setHttpReferrer("http://code.google.com/p/google-api-translate-java/");
        GoogleAPI.setKey("AIzaSyAbr8K-aiuxt8h-dK_vYL12QVpePQgQrpk");
        }
    });
}

// Variables declaration - do not modify                     
private javax.swing.JButton jButtonEspIng;
private javax.swing.JButton jButtonIngEsp;
private javax.swing.JTextField jTextFieldOri;
private javax.swing.JTextField jTextFieldTrad;
// End of variables declaration                   
 }

If you could help me! Thanks.