Fix build with wxGTK 3.0

--- src/common/myintl.cpp
+++ src/common/myintl.cpp
@@ -1060,7 +1060,7 @@ static wxString GetFullSearchPath(const wxChar *lang)
     wxString wxp = wxGetInstallPrefix();
     if ( !wxp.empty() )
     {
-        wxp = GetMsgCatalogSubdirs(wxp + _T("/share/locale"), lang);
+        wxp = GetMsgCatalogSubdirs((wxp + _T("/share/locale")).wchar_str(), lang);
         if ( paths.Index(wxp) == wxNOT_FOUND )
             paths.Add(wxp);
     }