Revert to English locale if the system default is not available

See #1525

Author: cmaglie

app/src/processing/app/Preferences.java

@@ -270,8 +270,8 @@ static protected void init(String commandLinePrefs) {
     try {
       I18n.init(Preferences.get("editor.languages.current"));
     } catch (MissingResourceException e) {
-      I18n.init("");
-      Preferences.set("editor.languages.current", "");
+      I18n.init("en");
+      Preferences.set("editor.languages.current", "en");
     }
 
     // set some other runtime constants (not saved on preferences file)

build/shared/revisions.txt

@@ -1,6 +1,9 @@
 
 ARDUINO 1.5.4 BETA
 
+[ide]
+* Revert to English locale if the system default is not available
+
 [libraries]
 * sam: fixed wrong SPI initialization (noblepepper)