diff --git a/core/src/jsonpp.cpp b/core/src/jsonpp.cpp
index 69c791c2cc..cfde2da976 100644
--- a/core/src/jsonpp.cpp
+++ b/core/src/jsonpp.cpp
@@ -13,7 +13,7 @@
 #include <limits>
 
 #include "jsonpp.hpp"
-
+#include "utfcodec.hpp"
 
 #if defined(_MSC_VER)
 #define FORMAT_INTMAX "%lli"
@@ -105,6 +105,15 @@ json & json::operator << (json::string s) throw()
     return *this;
 }
 
+json & json::operator <<(const char16_t* s) throw()
+{
+  std::u16string str16(s);
+  std::string str = convert<char16_t, char>(str16);
+
+  (*this) << str;
+  return *this;
+}
+
 json & json::operator << (json::number f) throw()
 {
     context(seq);
diff --git a/core/src/jsonpp.hpp b/core/src/jsonpp.hpp
index 985e7af9f6..d97afe50a6 100644
--- a/core/src/jsonpp.hpp
+++ b/core/src/jsonpp.hpp
@@ -20,8 +20,8 @@
 class json
 {
     // Prevent copying
-    json(const json &);
-    json & operator = (const json &);
+    json(const json &) = delete;
+    json & operator = (const json &) = delete;
 
     typedef void (*_context_t)(json &);
 
@@ -62,6 +62,7 @@ public:
 
     auto & stream() const throw();
 
+    json & operator << (const char16_t*) throw();
     json & operator << (string) throw();
     json & operator << (number) throw();
     json & operator << (integer) throw();
@@ -78,8 +79,8 @@ public:
 class json::closer
 {
     // Prevent copying.
-    closer(const closer &);
-    closer & operator = (const closer &);
+    closer(const closer &) = delete;
+    closer & operator = (const closer &) = delete;
 
     json * const    _j;
 public:
@@ -113,13 +114,17 @@ json & json::operator << (json::_context_t ctxt) throw()
     return *this;
 }
 
-template<typename C>
 inline
-json & operator << (json & j, std::basic_string<C> const & s) throw() { return j << json::string(convert<C,char>(s).c_str()); }
+json & operator << (json & j, std::string const & s) throw() { return j << json::string(s.c_str()); }
 
-template<typename C>
 inline
-json & operator << (json & j, C const * s) throw() { return j << json::string(convert<C,char>(s).c_str()); }
+json & operator << (json & j, std::string const * s) throw() { return j << json::string(s->c_str()); }
+
+inline
+json & operator << (json & j, std::u16string const & s) throw() { return j << json::string(convert<char16_t,char>(s).c_str()); }
+
+inline
+json & operator << (json & j, std::u16string const * s) throw() { return j << json::string(convert<char16_t,char>(*s).c_str()); }
 
 inline
 json & operator << (json & j, signed char d) throw()   { return j << json::integer(d); }
diff --git a/core/tests/unit/kmx/kmx_external_event.cpp b/core/tests/unit/kmx/kmx_external_event.cpp
index 9ebdccfc73..d5d48c8ad6 100644
--- a/core/tests/unit/kmx/kmx_external_event.cpp
+++ b/core/tests/unit/kmx/kmx_external_event.cpp
@@ -17,7 +17,6 @@
 
 #include <map>
 #include <iostream>
-#include <sstream>
 
 /**
  * This test will test the infrastructure around the external event processing
diff --git a/core/tests/unit/kmx/kmx_imx.cpp b/core/tests/unit/kmx/kmx_imx.cpp
index 1972d9dc26..12b3bc9455 100644
--- a/core/tests/unit/kmx/kmx_imx.cpp
+++ b/core/tests/unit/kmx/kmx_imx.cpp
@@ -14,10 +14,10 @@
 #include <test_assert.h>
 #include <test_color.h>
 #include "../emscripten_filesystem.h"
+#include "utfcodec.hpp"
 
 #include <map>
 #include <iostream>
-#include <sstream>
 
 /** This test will test the infrastructure around IMX third party librays
  *  and callback. The functions tested are:
@@ -172,13 +172,15 @@ void test_imx_list(const km::core::path &source_file){
 
   // This keyboard has 4 function names from 2 different libraries in the stores
   km_core_keyboard_imx *imx_rule_it = kb_imx_list;
-  std::stringstream extracted_library_function;
   auto x = 0;
   for (; imx_rule_it->library_name; ++imx_rule_it) {
-    extracted_library_function << imx_rule_it->library_name << ":" << imx_rule_it->function_name;
-    assert(extracted_library_function.str() == expected_imx_map[imx_rule_it->imx_id] );
-    g_extract_imx_map[imx_rule_it->imx_id] = extracted_library_function.str();
-    extracted_library_function.str("");
+    std::u16string str;
+    str.append(imx_rule_it->library_name);
+    str.append(u":");
+    str.append(imx_rule_it->function_name);
+    auto extracted_library_function = convert<km_core_cu,char>(str);
+    assert(extracted_library_function == expected_imx_map[imx_rule_it->imx_id] );
+    g_extract_imx_map[imx_rule_it->imx_id] = extracted_library_function;
     ++x;
   }