[LyX/2.1.x] Avoid requiring messages with empty language.

[Jean-Marc Lasgouttes]

commit 839f37317f1f4d910bb8bbfa416ebcbda7761947
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Wed Apr 15 15:27:05 2015 +0200

    Avoid requiring messages with empty language.
    
    This is a follow-up to commit 8aa2d6b1.

diff --git a/src/frontends/qt4/GuiApplication.cpp 
b/src/frontends/qt4/GuiApplication.cpp
index fdd9745..cf359d6 100644
--- a/src/frontends/qt4/GuiApplication.cpp
+++ b/src/frontends/qt4/GuiApplication.cpp
@@ -189,15 +189,13 @@ void setLocale()
        if (lyxrc.gui_language == "auto") {
                theLocale = QLocale::system();
                code = fromqstr(theLocale.name());
-               // Qt tries to outsmart us and transforms en_US to C.
-               if (code == "C")
-                       code = "en_US";
        } else {
                Language const * l = languages.getLanguage(lyxrc.gui_language);
-               code = l ? l->code() : string();
+               code = l ? l->code() : "C";
                theLocale = QLocale(toqstr(code));
        }
-       Messages::guiLanguage(code);
+       // Qt tries to outsmart us and transforms en_US to C.
+       Messages::guiLanguage((code == "C") ? "en_US" : code);
        QLocale::setDefault(theLocale);
        setlocale(LC_NUMERIC, "C");
 }