Unicode handling:

Removed the Perl dependencies on Encode, Encode::Locale and Unicode::Normalize.
Added dependency on boost::locale.
Added encode_path, decode_path, normalize_utf8 functions to Slic3r.xs

Slic3r.xs has been made mostly utf8 safe by using the boost::nowide library,
thanks to @alexrj for the idea.

Simplified the encode_path / decode_path stuff:
wxWidgets are unicode already, so there is no need to decode_path() from it.
Perl / win32 interfacing is non-unicode, so decode_path() is executed
on ARGV just at the beginning of the perl scripts.

xs/src/libslic3r/Format/AMF.cpp

@@ -3,6 +3,8 @@
 #include <string>
 #include <expat/expat.h>
 
+#include <boost/nowide/cstdio.hpp>
+
 #include "../libslic3r.h"
 #include "../Model.hpp"
 #include "AMF.hpp"
@@ -480,7 +482,7 @@ bool load_amf(const char *path, Model *model)
         return false;
     }
 
-    FILE *pFile = ::fopen(path, "rt");
+    FILE *pFile = boost::nowide::fopen(path, "rt");
     if (pFile == nullptr) {
         printf("Cannot open file %s\n", path);
         return false;
@@ -522,7 +524,7 @@ bool load_amf(const char *path, Model *model)
 
 bool store_amf(const char *path, Model *model)
 {
-    FILE *file = ::fopen(path, "wb");
+    FILE *file = boost::nowide::fopen(path, "wb");
     if (file == nullptr)
         return false;
 

xs/src/libslic3r/Format/PRUS.cpp

@@ -2,6 +2,8 @@
 
 #include <string.h>
 
+#include <boost/nowide/convert.hpp>
+
 #include <wx/string.h>
 #include <wx/wfstream.h>
 #include <wx/zipstrm.h>
@@ -119,7 +121,14 @@ bool load_prus(const char *path, Model *model)
 {
     // To receive the content of the zipped 'scene.xml' file.
     std::vector<char>           scene_xml_data;
-    wxFFileInputStream          in(path);
+    wxFFileInputStream          in(
+#ifdef WIN32
+        // On Windows, convert to a 16bit unicode string.
+        boost::nowide::widen(path).c_str()
+#else
+        path
+#endif
+        );
     wxZipInputStream            zip(in);
     std::unique_ptr<wxZipEntry> entry;
     size_t                      num_models = 0;

xs/src/libslic3r/Format/objparser.cpp

@@ -1,6 +1,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include <boost/nowide/cstdio.hpp>
+
 #include "objparser.hpp"
 
 namespace ObjParser {
@@ -318,7 +320,7 @@ static bool obj_parseline(const char *line, ObjData &data)
 
 bool objparse(const char *path, ObjData &data)
 {
-	FILE *pFile = ::fopen(path, "rt");
+	FILE *pFile = boost::nowide::fopen(path, "rt");
 	if (pFile == 0)
 		return false;
 
@@ -446,7 +448,7 @@ bool loadvectornameidx(FILE *pFile, std::vector<T> &v)
 
 bool objbinsave(const char *path, const ObjData &data)
 {
-	FILE *pFile = ::fopen(path, "wb");
+	FILE *pFile = boost::nowide::fopen(path, "wb");
 	if (pFile == 0)
 		return false;
 
@@ -471,7 +473,7 @@ bool objbinsave(const char *path, const ObjData &data)
 
 bool objbinload(const char *path, ObjData &data)
 {
-	FILE *pFile = ::fopen(path, "rb");
+	FILE *pFile = boost::nowide::fopen(path, "rb");
 	if (pFile == 0)
 		return false;
 

xs/src/libslic3r/GCode.cpp

@@ -13,6 +13,10 @@
 #include <boost/date_time/local_time/local_time.hpp>
 #include <boost/foreach.hpp>
 
+#include <boost/nowide/iostream.hpp>
+#include <boost/nowide/cstdio.hpp>
+#include <boost/nowide/cstdlib.hpp>
+
 #include "SVG.hpp"
 
 #if 0
@@ -306,7 +310,33 @@ std::vector<std::pair<coordf_t, std::vector<GCode::LayerToPrint>>> GCode::collec
     return layers_to_print;
 }
 
-bool GCode::do_export(FILE *file, Print &print)
+bool GCode::do_export(Print *print, const char *path)
+{
+    // Remove the old g-code if it exists.
+    boost::nowide::remove(path);
+
+    std::string path_tmp(path);
+    path_tmp += ".tmp";
+
+    FILE *file = boost::nowide::fopen(path_tmp.c_str(), "wb");
+    if (file == nullptr)
+        return false;
+
+    bool result = this->_do_export(*print, file);
+    fclose(file);
+
+    if (result && boost::nowide::rename(path_tmp.c_str(), path) != 0) {
+        boost::nowide::cerr << "Failed to remove the output G-code file from " << path_tmp << " to " << path
+            << ". Is " << path_tmp << " locked?" << std::endl;
+        result = false;
+    }
+
+    if (! result)
+        boost::nowide::remove(path_tmp.c_str());
+    return result;
+}
+
+bool GCode::_do_export(Print &print, FILE *file)
 {
     // How many times will be change_layer() called?
     // change_layer() in turn increments the progress bar status.

xs/src/libslic3r/GCode.hpp

@@ -126,7 +126,7 @@ public:
         {}
     ~GCode() {}
 
-    bool            do_export(FILE *file, Print &print);
+    bool            do_export(Print *print, const char *path);
 
     // Exported for the helper classes (OozePrevention, Wipe) and for the Perl binding for unit tests.
     const Pointf&   origin() const { return m_origin; }
@@ -146,6 +146,8 @@ public:
     void            apply_print_config(const PrintConfig &print_config);
 
 protected:
+    bool            _do_export(Print &print, FILE *file);
+
     // Object and support extrusions of the same PrintObject at the same print_z.
     struct LayerToPrint
     {

xs/src/libslic3r/Model.cpp

@@ -10,6 +10,7 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/filesystem.hpp>
+#include <boost/nowide/iostream.hpp>
 
 namespace Slic3r {
 
@@ -739,7 +740,7 @@ void ModelObject::print_info() const
 {
     using namespace std;
     cout << fixed;
-    cout << "[" << boost::filesystem::path(this->input_file).filename().string() << "]" << endl;
+    boost::nowide::cout << "[" << boost::filesystem::path(this->input_file).filename().string() << "]" << endl;
     
     TriangleMesh mesh = this->raw_mesh();
     mesh.check_topology();

xs/src/libslic3r/SVG.cpp

@@ -1,6 +1,8 @@
 #include "SVG.hpp"
 #include <iostream>
 
+#include <boost/nowide/cstdio.hpp>
+
 #define COORD(x) ((float)unscale((x))*10)
 
 namespace Slic3r {
@@ -8,7 +10,7 @@ namespace Slic3r {
 bool SVG::open(const char* afilename)
 {
     this->filename = afilename;
-    this->f = fopen(afilename, "w");
+    this->f = boost::nowide::fopen(afilename, "w");
     if (this->f == NULL)
         return false;
     fprintf(this->f,
@@ -27,7 +29,7 @@ bool SVG::open(const char* afilename, const BoundingBox &bbox, const coord_t bbo
     this->filename = afilename;
     this->origin   = bbox.min - Point(bbox_offset, bbox_offset);
     this->flipY    = aflipY;
-    this->f        = ::fopen(afilename, "w");
+    this->f        = boost::nowide::fopen(afilename, "w");
     if (f == NULL)
         return false;
     float w = COORD(bbox.max.x - bbox.min.x + 2 * bbox_offset);

xs/src/libslic3r/Utils.hpp

@@ -6,6 +6,10 @@ namespace Slic3r {
 extern void set_logging_level(unsigned int level);
 extern void trace(unsigned int level, const char *message);
 
+extern std::string encode_path(const char *src);
+extern std::string decode_path(const char *src);
+extern std::string normalize_utf8_nfc(const char *src);
+
 // Compute the next highest power of 2 of 32-bit v
 // http://graphics.stanford.edu/~seander/bithacks.html
 template<typename T>

xs/src/libslic3r/utils.cpp

@@ -1,7 +1,21 @@
+#include <locale>
+
 #include <boost/log/core.hpp>
 #include <boost/log/trivial.hpp>
 #include <boost/log/expressions.hpp>
 
+#include <boost/locale.hpp>
+
+#include <boost/nowide/integration/filesystem.hpp>
+#include <boost/nowide/convert.hpp>
+
+#ifdef WIN32
+extern "C" {
+__declspec(dllimport) int WideCharToMultiByte(unsigned int, unsigned long, wchar_t const *, int, char *, int, char const *, int *);
+__declspec(dllimport) int MultiByteToWideChar(unsigned int, unsigned long, char const *, int, wchar_t *, int);
+}
+#endif /* WIN32 */
+
 namespace Slic3r {
 
 static boost::log::trivial::severity_level logSeverity = boost::log::trivial::error;
@@ -30,9 +44,13 @@ void set_logging_level(unsigned int level)
 }
 
 // Force set_logging_level(<=error) after loading of the DLL.
-static struct SetLoggingLevelOnInit {
-    SetLoggingLevelOnInit() { set_logging_level(1); }
-} g_SetLoggingLevelOnInit;
+// Switch boost::filesystem to utf8.
+static struct RunOnInit {
+    RunOnInit() { 
+        boost::nowide::nowide_filesystem();
+        set_logging_level(1);
+    }
+} g_RunOnInit;
 
 void trace(unsigned int level, const char *message)
 {
@@ -56,6 +74,46 @@ void trace(unsigned int level, const char *message)
         (::boost::log::keywords::severity = severity)) << message;
 }
 
+std::string encode_path(const char *src)
+{    
+#ifdef WIN32
+    // Convert the source utf8 encoded string to a wide string.
+    std::wstring wstr_src = boost::nowide::widen(src);
+    if (wstr_src.length() == 0)
+        return std::string();
+    // Convert a wide string to a local code page.
+    int size_needed = ::WideCharToMultiByte(0, 0, wstr_src.data(), (int)wstr_src.size(), nullptr, 0, nullptr, nullptr);
+    std::string str_dst(size_needed, 0);
+    ::WideCharToMultiByte(0, 0, wstr_src.data(), (int)wstr_src.size(), const_cast<char*>(str_dst.data()), size_needed, nullptr, nullptr);
+    return str_dst;
+#else /* WIN32 */
+    return src;
+#endif /* WIN32 */
+}
+
+std::string decode_path(const char *src)
+{  
+#ifdef WIN32
+    int len = strlen(src);
+    if (len == 0)
+        return std::string();
+    // Convert the string encoded using the local code page to a wide string.
+    int size_needed = ::MultiByteToWideChar(0, 0, src, len, nullptr, 0);
+    std::wstring wstr_dst(size_needed, 0);
+    ::MultiByteToWideChar(0, 0, src, len, const_cast<wchar_t*>(wstr_dst.data()), size_needed);
+    // Convert a wide string to utf8.
+    return boost::nowide::narrow(wstr_dst.c_str());
+#else /* WIN32 */
+    return src;
+#endif /* WIN32 */
+}
+
+std::string normalize_utf8_nfc(const char *src)
+{
+    static std::locale locale_utf8("en_US.UTF-8");
+    return boost::locale::normalize(src, boost::locale::norm_nfc, locale_utf8);
+}
+
 } // namespace Slic3r
 
 #ifdef SLIC3R_HAS_BROKEN_CROAK