Add wxUILocale with minimal functionality

Use it in the sample to show what (little) it can do right now.

src/common/uilocale.cpp

@@ -0,0 +1,90 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        src/common/uilocale.cpp
+// Purpose:     wxUILocale implementation
+// Author:      Vadim Zeitlin
+// Created:     2021-07-31
+// Copyright:   (c) 2021 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+// ============================================================================
+// declarations
+// ============================================================================
+
+// ----------------------------------------------------------------------------
+// headers
+// ----------------------------------------------------------------------------
+
+// for compilers that support precompilation, includes "wx.h".
+#include "wx/wxprec.h"
+
+#if wxUSE_INTL
+
+#include "wx/uilocale.h"
+
+#include "wx/private/uilocale.h"
+
+// ----------------------------------------------------------------------------
+// global variables
+// ----------------------------------------------------------------------------
+
+// This static global variable doesn't need to be protected from concurrent
+// access as it's only supposed to be used from the UI thread.
+/* static */
+wxUILocale wxUILocale::ms_current;
+
+// ============================================================================
+// implementation
+// ============================================================================
+
+/* static */
+bool wxUILocale::UseDefault()
+{
+    // We don't attempt to optimize this function by checking whether
+    // ms_current is already set to the user default locale, as we're
+    // supposed to be called just once during the program lifetime anyhow.
+
+    wxUILocaleImpl* const impl = wxUILocaleImpl::CreateUserDefault();
+    if ( !impl )
+        return false;
+
+    ms_current.SetImpl(impl);
+
+    return true;
+}
+
+/* static */
+const wxUILocale& wxUILocale::GetCurrent()
+{
+    // We initialize it on demand.
+    if ( !ms_current.m_impl )
+    {
+        ms_current.SetImpl(wxUILocaleImpl::CreateStdC());
+    }
+
+    return ms_current;
+}
+
+void wxUILocale::SetImpl(wxUILocaleImpl* impl)
+{
+    delete m_impl;
+
+    m_impl = impl;
+}
+
+wxString wxUILocale::GetName() const
+{
+    return m_impl->GetName();
+}
+
+wxString wxUILocale::GetInfo(wxLocaleInfo index, wxLocaleCategory cat) const
+{
+    return m_impl->GetInfo(index, cat);
+}
+
+wxUILocale::~wxUILocale()
+{
+    delete m_impl;
+}
+
+#endif // wxUSE_INTL