[Languages] Add new information to system language page.

- Add top Intro preference
 - Add footer preference
 - Add sub string to language picker
 - Modify title of app locale pages

Bug: 242182598 Add information to system language page.
Bug: 241600418 [Panlingual] Change strings on App languages
Test: Maunal test
Change-Id: I9bca8911e8e70c97c273294b3c9d1d73d4ea0cb2

src/com/android/settings/localepicker/LocaleDragCell.java

@@ -33,6 +33,7 @@ class LocaleDragCell extends RelativeLayout {
     private CheckBox mCheckbox;
     private TextView mMiniLabel;
     private TextView mLocalized;
+    private TextView mCurrentDefault;
     private ImageView mDragHandle;
 
     public LocaleDragCell(Context context, AttributeSet attrs) {
@@ -44,6 +45,7 @@ class LocaleDragCell extends RelativeLayout {
         super.onFinishInflate();
         mLabel = (TextView) findViewById(R.id.label);
         mLocalized = (TextView) findViewById(R.id.l10nWarn);
+        mCurrentDefault = (TextView) findViewById(R.id.default_locale);
         mMiniLabel = (TextView) findViewById(R.id.miniLabel);
         mCheckbox = (CheckBox) findViewById(R.id.checkbox);
         mDragHandle = (ImageView) findViewById(R.id.dragHandle);
@@ -100,6 +102,14 @@ class LocaleDragCell extends RelativeLayout {
         invalidate();
     }
 
+    /**
+     * Indicate current locale is system default.
+     */
+    public void setCurrentDefault(boolean isCurrentDefault) {
+        mCurrentDefault.setVisibility(isCurrentDefault ? VISIBLE : GONE);
+        invalidate();
+    }
+
     public ImageView getDragHandle() {
         return mDragHandle;
     }