diff --git a/app/src/main/java/net/gsantner/opoc/ui/LanguagePreference.java b/app/src/main/java/net/gsantner/opoc/ui/LanguagePreference.java
index 03e64c2f..5a41be6d 100644
--- a/app/src/main/java/net/gsantner/opoc/ui/LanguagePreference.java
+++ b/app/src/main/java/net/gsantner/opoc/ui/LanguagePreference.java
@@ -19,7 +19,7 @@
 
 buildConfigField("String[]", "APPLICATION_LANGUAGES", '{' + getUsedAndroidLanguages().collect {"\"${it}\""}.join(",")  + '}')
 
-@SuppressWarnings(["UnnecessaryQualifiedReference", "SpellCheckingInspection"])
+@SuppressWarnings(["UnnecessaryQualifiedReference", "SpellCheckingInspection", "GroovyUnusedDeclaration"])
 static String[] getUsedAndroidLanguages() {
     Set<String> langs = new HashSet<>()
     new File('.').eachFileRecurse(groovy.io.FileType.DIRECTORIES) {
@@ -28,7 +28,6 @@ static String[] getUsedAndroidLanguages() {
             new File(it.toString()).eachFileRecurse(groovy.io.FileType.FILES) {
                 if (it.name.toLowerCase().endsWith(".xml") && it.getCanonicalFile().getText('UTF-8').contains("<string")) {
                     langs.add(foldername.replace("values-", ""))
-
                 }
             }
         }
@@ -147,8 +146,8 @@ public class LanguagePreference extends ListPreference {
         String country = locale.getDisplayCountry(locale);
         String language = locale.getDisplayLanguage(locale);
         return locale.getDisplayLanguage(Locale.ENGLISH)
-                + " (" + language.substring(0, 1).toUpperCase() + language.substring(1)
-                + ((!country.isEmpty() && !country.toLowerCase().equals(language.toLowerCase())) ? (", " + country) : "")
+                + " (" + language.substring(0, 1).toUpperCase(Locale.getDefault()) + language.substring(1)
+                + ((!country.isEmpty() && !country.toLowerCase(Locale.getDefault()).equals(language.toLowerCase(Locale.getDefault()))) ? (", " + country) : "")
                 + ")";
     }
 
diff --git a/app/src/main/java/net/gsantner/opoc/util/ContextUtils.java b/app/src/main/java/net/gsantner/opoc/util/ContextUtils.java
index a27c3361..261f8651 100644
--- a/app/src/main/java/net/gsantner/opoc/util/ContextUtils.java
+++ b/app/src/main/java/net/gsantner/opoc/util/ContextUtils.java
@@ -54,7 +54,6 @@ import android.text.SpannableString;
 import android.text.Spanned;
 import android.text.TextUtils;
 import android.text.method.LinkMovementMethod;
-import android.text.style.ForegroundColorSpan;
 import android.util.DisplayMetrics;
 import android.view.Menu;
 import android.view.MenuItem;
@@ -446,7 +445,7 @@ public class ContextUtils {
 
     public File writeImageToFileDetectFormat(File imageFile, Bitmap image, int quality) {
         CompressFormat format = CompressFormat.JPEG;
-        String lc = imageFile.getAbsolutePath().toLowerCase();
+        String lc = imageFile.getAbsolutePath().toLowerCase(Locale.ROOT);
         if (lc.endsWith(".png")) {
             format = CompressFormat.PNG;
         }
@@ -544,4 +543,18 @@ public class ContextUtils {
         }
         return this;
     }
+
+    public void showRateOnGplayDialog() {
+        String pkgId = "details?id=" + _context.getPackageName();
+        Intent goToMarket = new Intent(Intent.ACTION_VIEW, Uri.parse("market://" + pkgId));
+        goToMarket.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY |
+                (Build.VERSION.SDK_INT >= 21 ? Intent.FLAG_ACTIVITY_NEW_DOCUMENT : Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET) |
+                Intent.FLAG_ACTIVITY_MULTIPLE_TASK);
+        try {
+            _context.startActivity(goToMarket);
+        } catch (ActivityNotFoundException e) {
+            _context.startActivity(new Intent(Intent.ACTION_VIEW,
+                    Uri.parse("http://play.google.com/store/apps/" + pkgId)));
+        }
+    }
 }