Settings has a Language row, for choosing Gearslip's language

Android 13 and later already let you pick it, but only from the
system's app settings, which few people find (#51).

gearslip/src/main/res/values-da/strings.xml

@@ -1,3 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
+    <string name="settings_language">Sprog</string>
+    <string name="settings_language_phone">Samme som telefonen</string>
 </resources>