Change wxLocaleIdent ctor to take char* rather than wxString

This is convenient, as it allows using a simple string such as "en" as
an argument to the functions taking wxLocaleIdent and rely on implicit
conversion, whereas previously explicitly writing either wxString("en")
or wxLocaleIdent("en") would be necessary.

include/wx/localedefs.h

@@ -118,8 +118,13 @@ public:
     // Leave language empty
     wxLocaleIdent() { }
 
-    // Construct name from language
-    wxLocaleIdent(const wxString& language) : m_language(language) { }
+    // Construct from language, i.e. a two-letter ISO 639-1 code (or a
+    // three-letter ISO 639-2 code if there is no ISO 639-1 code for this
+    // language).
+    wxLocaleIdent(const char* language)
+        : m_language(wxString::FromAscii(language))
+    {
+    }
 
     // Set language
     wxLocaleIdent& Language(const wxString& language)

interface/wx/uilocale.h

@@ -184,11 +184,14 @@ public:
     /**
         Constructor with language.
 
+        Note that this constructor is non-explicit, allowing to pass just a
+        simple string, such as "en", to functions taking wxLocaleIdent.
+
         @param language
             ISO 639 language code.
             See Language() for more detailed info.
     */
-    wxLocaleIdent(const wxString& language);
+    wxLocaleIdent(const char* language);
 
     /**
         Set language.