Adding extra row to the android default keyboard is not possible for this you have to go to the custom keyboard..Custom keyboard is not much difficult to understand here is the best example of android custom keyboards..
1.Custom keyboard example-1
2.Custom keyboard example-2
Once go to the xml file in the res/xml folder and define keys whatever you want..and no of rows and columns for keyboard..
In your layout definig the keyboardview set android:keyBackground="@drawable/keyboardview_selector"
color whatever you want..
<android.inputmethodservice.KeyboardView
android:id="@+id/keyboardview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginBottom="10dp"
android:background="@android:color/transparent"
android:focusable="true"
android:focusableInTouchMode="true"
android:keyBackground="@drawable/keyboardview_selector" />