Add wxUILocale with minimal functionality

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

src/unix/uilocale.cpp

@@ -0,0 +1,91 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        src/unix/uilocale.cpp
+// Purpose:     wxUILocale implementation for Unix systems
+// Author:      Vadim Zeitlin
+// Created:     2021-08-01
+// 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/private/uilocale.h"
+
+#include "wx/intl.h"
+
+#include <locale.h>
+
+namespace
+{
+
+// ----------------------------------------------------------------------------
+// wxUILocale implementation using standard Unix/C functions
+// ----------------------------------------------------------------------------
+
+class wxUILocaleImplUnix : public wxUILocaleImpl
+{
+public:
+    // Locale argument may be NULL to not change it at all.
+    explicit wxUILocaleImplUnix(const char* locale);
+
+    wxString GetName() const wxOVERRIDE;
+    wxString GetInfo(wxLocaleInfo index, wxLocaleCategory cat) const wxOVERRIDE;
+
+private:
+    wxDECLARE_NO_COPY_CLASS(wxUILocaleImplUnix);
+};
+
+} // anonymous namespace
+
+// ============================================================================
+// implementation
+// ============================================================================
+
+wxUILocaleImplUnix::wxUILocaleImplUnix(const char* locale)
+{
+    if ( locale )
+        setlocale(LC_ALL, locale);
+}
+
+wxString
+wxUILocaleImplUnix::GetName() const
+{
+    return wxString::FromAscii(setlocale(LC_ALL, NULL));
+}
+
+wxString
+wxUILocaleImplUnix::GetInfo(wxLocaleInfo index, wxLocaleCategory cat) const
+{
+    // Currently we rely on the user code not calling setlocale() itself, so
+    // that the current locale is still the same as was set in the ctor.
+    //
+    // If this assumption turns out to be wrong, we could use wxLocaleSetter to
+    // temporarily change the locale here (maybe only if setlocale(NULL) result
+    // differs from the expected one).
+    return wxLocale::GetInfo(index, cat);
+}
+
+/* static */
+wxUILocaleImpl* wxUILocaleImpl::CreateStdC()
+{
+    return new wxUILocaleImplUnix(NULL);
+}
+
+/* static */
+wxUILocaleImpl* wxUILocaleImpl::CreateUserDefault()
+{
+    return new wxUILocaleImplUnix("");
+}
+
+#endif // wxUSE_INTL