[LyX/master] Fix setting Interlingua as GUI language

[Jean-Marc Lasgouttes]

commit 8aa2d6b18415659e147bfb4039e371a3277226d5
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Tue Mar 17 11:34:28 2015 +0100

    Fix setting Interlingua as GUI language
    
    The problem came from the fact that Qt associates Interlingua to locale C.
    Now, we do not rely anymore on the Qt locale to set the language. I suspect 
that the problem will still exist if the system locale is ia_IA.
    
    Fixes bug #9267.

diff --git a/src/frontends/qt4/GuiApplication.cpp 
b/src/frontends/qt4/GuiApplication.cpp
index 39b73cf..f858d85 100644
--- a/src/frontends/qt4/GuiApplication.cpp
+++ b/src/frontends/qt4/GuiApplication.cpp
@@ -192,16 +192,19 @@ frontend::Application * createApplication(int & argc, 
char * argv[])
 void setLocale()
 {
        QLocale theLocale;
+       string code;
        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);
-               string const code = l ? l->code() : string();
+               code = l ? l->code() : string();
                theLocale = QLocale(toqstr(code));
        }
-       string const code = fromqstr(theLocale.name());
-       // Qt tries to outsmart us and transforms en_US to C.
-       Messages::guiLanguage((code == "C") ? "en_US" : code);
+       Messages::guiLanguage(code);
        QLocale::setDefault(theLocale);
        setlocale(LC_NUMERIC, "C");
 }