add korean supports (#338)

* add korean supports

It might have some typos.

* translated one more sentence

* some fixes

"..." was replaced “…” with ellipsis character and some was fixed

* few modifications

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

@@ -24,6 +24,7 @@
             <item>Japanese</item>
             <item>Русский</item>
             <item>Nederlands</item>
+            <item>Korean</item>
     </string-array>
     <string-array name="language_values" translatable="false">
             <item>default</item>
@@ -32,6 +33,7 @@
             <item>ja</item>
             <item>ru</item>
             <item>nl</item>
+            <item>ko</item>
     </string-array>
 
     <string-array name="decoder_names">