See bug 77341

static gchar*
strdup_convert (const gchar *string,
		const gchar *charset)
{
  if (!g_utf8_validate (string, -1, NULL))
    return g_strconcat ("[Invalid UTF-8] ", string, NULL);
  else
    return g_convert_with_fallback (string, -1, charset, "UTF-8", "?",
NULL, NULL, NULL);
}

Has problesm because g_convert_with_fallback() can fail even if string
is valid UTF-8, though the most common reason for this would be that
there is some problem with the system... e.g., that g_get_charset()
is not working correctly.