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/java/eu/kanade/tachiyomi/util/LocaleHelper.kt

@@ -0,0 +1,48 @@
+package eu.kanade.tachiyomi.util
+
+import android.app.Application
+import android.content.res.Configuration
+import android.os.Build
+import android.view.ContextThemeWrapper
+import eu.kanade.tachiyomi.data.preference.PreferencesHelper
+import uy.kohesive.injekt.injectLazy
+import java.util.Locale
+
+
+object LocaleHelper {
+
+    private val preferences: PreferencesHelper by injectLazy()
+    private var pLocale = Locale(LocaleHelper.intToLangCode(preferences.lang()))
+
+    fun setLocale(locale: Locale) {
+        pLocale = locale
+        Locale.setDefault(pLocale)
+    }
+
+    fun updateCfg(wrapper: ContextThemeWrapper) {
+        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1){
+            val config = Configuration()
+            config.setLocale(pLocale)
+            wrapper.applyOverrideConfiguration(config)
+        }
+    }
+
+    fun updateCfg(app: Application, config: Configuration){
+        if(Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
+            config.locale = pLocale
+            app.baseContext.resources.updateConfiguration(config, app.baseContext.resources.displayMetrics)
+        }
+    }
+
+    fun intToLangCode(i: Int): String {
+        return when(i){
+            1 -> "en"
+            2 -> "es"
+            3 -> "it"
+            4 -> "pt"
+            // System Language
+            else -> ""
+        }
+    }
+
+}