How to display utf8 encoded font - opengl

Question

I want to display utf8 encoded font in my program but the output is only Question marks.
The following code works fine with English fonts but when i try other regional fonts i only get question Marks.
I am using Freetype to load fonts.
Please have a look at my code and let me know how i can use UTF8 Fonts in opengl.
This is my first project with handling fonts so any reference read or advice would be highly valuable to me.
Constructor for font object
Font::Font( const Shader& shader ) : Geometry()
{
this->fontSize = 40;
this->shader = shader;
this->Kerning = 3.0;
this->TextureHeight = 0.0;
this->TextureWidth = 0.0;
this->quadVAO = 0;
stdstrTxt = "डेमो दृश्य"; // The utf8 encoded font
glGenVertexArrays(1, &this->VAO);
glGenBuffers(1, &this->VBO);
glBindVertexArray(this->VAO);
glBindBuffer(GL_ARRAY_BUFFER, this->VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 6 * 5, NULL, GL_DYNAMIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)(3 * sizeof(float)));
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
}
Loading font as texture
void Font::Load(std::string font )
{// First clear the previously loaded Characters
this->Characters.clear(); // std::map for strorinf chars
// Then initialize and load the FreeType library
FT_Library ft;
if (FT_Init_FreeType(&ft)) // All functions return a value different than 0 whenever an error occurred
std::cout << "ERROR::FREETYPE: Could not init FreeType Library" << std::endl;
// Load font as face
FT_Face face;
if (FT_New_Face(ft, font.c_str(), 0, &face))
std::cout << "ERROR::FREETYPE: Failed to load font" << std::endl;
// Set size to load glyphs as
FT_Set_Pixel_Sizes(face, 0, fontSize);
FT_Select_Charmap(face, ft_encoding_unicode);
// Disable byte-alignment restriction
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
// Then for the first 128 ASCII characters, pre-load/compile their characters and store them
for (GLubyte c = 0; c < 128; c++)
{
// Load character glyph
if (FT_Load_Char(face, c, FT_LOAD_RENDER))
{
std::cout << "ERROR::FREETYTPE: Failed to load Glyph" << std::endl;
continue;
}
// Get the Image width and height value
this->TextureWidth = face->glyph->bitmap.width;
this->TextureHeight = face->glyph->bitmap.rows;
// Generate texture
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(
GL_TEXTURE_2D,
0,
GL_RED,
face->glyph->bitmap.width,
face->glyph->bitmap.rows,
0,
GL_RED,
GL_UNSIGNED_BYTE,
face->glyph->bitmap.buffer
);
// Set texture options
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// Now store character for later use
Character character = {
texture,
glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),
glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top),
face->glyph->advance.x
};
Characters.insert(std::pair<GLchar, Character>(c, character));
}
glBindTexture(GL_TEXTURE_2D, 0);
// Destroy FreeType once we're finished
FT_Done_Face(face);
FT_Done_FreeType(ft);
}