added mostly-proper Unicode support.

Note, the single character decoding obviously won't work with multi code-unit characters.
To fix that, the code-unit by code-unit decoding would need to be modified to detect code-units in the surrogate range, and continue decoding more code-units until a complete code-point is found.
Fortunately, most languages are within the Basic Multilingual Plane.

src/USBAnalyzerResults.cpp

@@ -1,7 +1,8 @@
 #include <iostream>
 #include <fstream>
 #include <algorithm>
-
+#include <locale>
+#include <codecvt>
 #include <stdio.h>
 
 #include <AnalyzerHelpers.h>
@@ -517,7 +518,13 @@ void GetCtrlTransFrameDesc( const Frame& frm, DisplayBase display_base, std::vec
     }
     else if( formatter == Fld_Wchar )
     {
-        desc = std::string( " char='" ) + char( val & 0xff ) + '\'';
+        // utf-8 encode the utf-16 character.
+        std::u16string utf_16_str;
+        char16_t u16_char = static_cast<char16_t>( val );
+        utf_16_str.push_back( u16_char );
+        std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
+        std::string utf8_str = convert.to_bytes( utf_16_str );
+        desc = std::string( " char='" ) + utf8_str + '\'';
     }
     else if( formatter == Fld_wLANGID )
     {

src/USBControlTransfers.cpp

@@ -1,6 +1,8 @@
 #include <algorithm>
 #include <cassert>
 #include <iostream>
+#include <locale>
+#include <codecvt>
 
 #include <AnalyzerChannelData.h>
 #include <AnalyzerHelpers.h>
@@ -371,12 +373,13 @@ bool USBControlTransferParser::ParseStringDescriptor()
     else
     {
         if( mParsedOffset == 2 )
-            stringDescriptor.clear();
+            utf16StringDescriptor.clear();
 
         // the actual UNICODE string
         while( mDescBytes > mParsedOffset && mPacketDataBytes > mPacketOffset )
         {
-            stringDescriptor += ( char )pPacket->GetDataPayload( mPacketOffset, 1 );
+            char16_t code_unit = static_cast<char16_t>( pPacket->GetDataPayload( mPacketOffset, 2 ) );
+            utf16StringDescriptor.push_back( code_unit );
 
             pResults->AddFrame( pPacket->GetDataPayloadField( mPacketOffset, 2, mAddress, "wchar", Fld_Wchar ) );
             mPacketOffset += 2;
@@ -386,7 +389,9 @@ bool USBControlTransferParser::ParseStringDescriptor()
         // do we have the entire string?
         if( mDescBytes == mParsedOffset )
         {
-            pResults->AddStringDescriptor( mAddress, mRequest.GetRequestedDescriptorIndex(), stringDescriptor );
+            std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
+            std::string utf8_string_descriptor = convert.to_bytes( utf16StringDescriptor );
+            pResults->AddStringDescriptor( mAddress, mRequest.GetRequestedDescriptorIndex(), utf8_string_descriptor );
         }
     }
     // return true if we've finished parsing the string descriptor, according to the parsed bLength

src/USBControlTransfers.h

@@ -233,7 +233,8 @@ class USBControlTransferParser
 
     USBRequest mRequest;
 
-    std::string stringDescriptor;
+    std::u16string utf16StringDescriptor;
+
 
     // these are only valid during a ParsePacket call, and invalid before and after
     USBPacket* pPacket;