[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

tests/unit/src/com/android/settings/localepicker/LocaleHelperPreferenceControllerTest.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.localepicker;
+
+import static org.mockito.Mockito.anyString;
+import static org.mockito.Mockito.verify;
+
+import android.content.Context;
+import android.os.Looper;
+
+import androidx.test.core.app.ApplicationProvider;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+
+import com.android.settingslib.widget.FooterPreference;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+@RunWith(AndroidJUnit4.class)
+public class LocaleHelperPreferenceControllerTest {
+    private Context mContext;
+    private LocaleHelperPreferenceController mLocaleHelperPreferenceController;
+
+    @Mock
+    private FooterPreference mMockFooterPreference;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        if (Looper.myLooper() == null) {
+            Looper.prepare();
+        }
+        mContext = ApplicationProvider.getApplicationContext();
+        mLocaleHelperPreferenceController = new LocaleHelperPreferenceController(mContext);
+    }
+
+    @Test
+    public void updateFooterPreference_setFooterPreference_hasClickAction() {
+        mLocaleHelperPreferenceController.updateFooterPreference(mMockFooterPreference);
+        verify(mMockFooterPreference).setLearnMoreText(anyString());
+    }
+}