Implement language switcher (#563)

* Implement language switching using BaseActivity

* Add requested changes

* Cleanup App.kt Imports and add pref_language_key

* Acutally use @string for key

* Use string resource for language preference title

app/src/main/res/values/arrays.xml

@@ -188,4 +188,20 @@
         <item>2</item>
     </string-array>
 
+    <string-array name="languages">
+        <item>@string/system_default</item>
+        <item>@string/english</item>
+        <item>@string/spanish</item>
+        <item>@string/italian</item>
+        <item>@string/portuguese</item>
+    </string-array>
+
+    <string-array name="languages_values">
+        <item>0</item>
+        <item>1</item>
+        <item>2</item>
+        <item>3</item>
+        <item>4</item>
+    </string-array>
+
 </resources>

app/src/main/res/values/keys.xml

@@ -21,6 +21,7 @@
     <string name="pref_theme_key">pref_theme_key</string>
     <string name="pref_library_update_restriction_key">library_update_restriction</string>
     <string name="pref_start_screen_key">start_screen</string>
+    <string name="pref_language_key">language</string>
 
     <string name="pref_default_viewer_key">pref_default_viewer_key</string>
     <string name="pref_image_scale_type_key">pref_image_scale_type_key</string>

app/src/main/res/values/strings.xml

@@ -111,6 +111,14 @@
     <string name="light_theme">Main theme</string>
     <string name="dark_theme">Dark theme</string>
     <string name="pref_start_screen">Start screen</string>
+    <string name="pref_language">Language</string>
+
+      <!-- Languages -->
+    <string name="system_default">System Default</string>
+    <string name="english">English</string>
+    <string name="spanish">Spanish</string>
+    <string name="italian">Italian</string>
+    <string name="portuguese">Portuguese</string>
 
       <!-- Reader section -->
     <string name="pref_fullscreen">Fullscreen</string>