Letter icons for non latin characters

app/src/main/java/eu/faircode/email/Helper.java

@@ -404,6 +404,12 @@ public class Helper {
         return df.format(bytes / Math.pow(unit, exp)) + " " + pre + "B";
     }
 
+    static boolean isPrintableChar(char c) {
+        Character.UnicodeBlock block = Character.UnicodeBlock.of(c);
+        if (block == null || block == Character.UnicodeBlock.SPECIALS)
+            return false;
+        return !Character.isISOControl(c);
+    }
     // https://issuetracker.google.com/issues/37054851
 
     static DateFormat getTimeInstance(Context context) {

app/src/main/java/eu/faircode/email/ImageHelper.java

@@ -115,7 +115,7 @@ class ImageHelper {
         String letter = null;
         for (int i = 0; i < name.length(); i++) {
             char kar = name.charAt(i);
-            if (Character.isAlphabetic(kar)) {
+            if (Helper.isPrintableChar(kar)) {
                 letter = name.substring(i, i + 1).toUpperCase();
                 break;
             }