C++ tolower для русского языка.

boost::locale::to_lower

Sentence::Sentence(std::string sntc)
	{       
        orSentence = sntc;
        std::vector<std::string> orWords;
        std::vector<std::string> words;
        boost::split(words, orSentence, boost::is_any_of("\t "));
        //this->words = words;
        for(std::string word : words)
        {

            boost::algorithm::trim(word);
            boost::algorithm::to_lower(word);
            /*//Delete from word \r
            if (!word.empty() && word[word.size() - 1] == '\r')
                word.erase(word.size() - 1);*/
            FoundWord foundWord ;
            foundWord = Vocabulary::GetWord(word);
            if(foundWord.isFound == false)
                continue;
            else
                orWords.push_back (foundWord.word.originalWord);
        }
		
	}

#include<iostream>
#include<iomanip> // std::endl
#include<string>
#include<algorithm> // transform

int main()
{
        std::locale::global(std::locale("en_US.utf8"));
        std::wcout.imbue(std::locale());

        std::wstring wstr=L"ПривЕт";

        transform(wstr.begin(), wstr.end(), wstr.begin(), towlower);

        std::wcout << wstr << std::endl;
}

terminate called after throwing an instance of 'std::runtime_error'
  what():  locale::facet::_S_create_c_locale name not valid

#include<iostream>
#include<iomanip> 
#include<string>
#include<algorithm> 

int main() {
   std::locale::global(std::locale(""));
   std::wcout.imbue(std::locale());
   auto& facet = std::use_facet<std::ctype<wchar_t>>(std::locale());
   std::wstring str = L"КУРВА, Я ПЕРДОЛЕ";
   std::wcout << str << std::endl;
   facet.tolower(&str[0], &str[0] + str.size());   
   std::wcout <<  str << std::endl;
}

$ g++ -std=c++11 pierdole.cpp 
$ ./a.out 
КУРВА, Я ПЕРДОЛЕ
курва, я пердоле