Font could be matched only when the family supports language, so glyph is not shown.

1) When we write text, Qt finds their code points and detects if they are in a font family (if not, load fallback font and then execute). 
2) If their glyphs are in the font family, Qt renders that. 
3) But at that point in Qt font engine, That has checked if the font family has "language" value that code points belong to.
4) That is, Qt can use only the font when the font supports not the code points we want, but also their language, 

static int match(int script, const QFontDef &request,
                 const QString &family_name, const QString &foundry_name,
                 QtFontDesc *desc, const QList<int> &blacklistedFamilies)
{
............
 for (int x = 0; x < db->count; ++x) {
        if (blacklistedFamilies.contains(x))
            continue;
        QtFontDesc test;
        test.family = db->families[x];

        if (!matchFamilyName(family_name, test.family))
            continue;

        test.family->ensurePopulated();

        // Check if family is supported in the script we want
        if (writingSystem != QFontDatabase::Any && !(test.family->writingSystems[writingSystem] & QtFontFamily::Supported))
            continue;

        // as we know the script is supported, we can be sure
 // to find a matching font here.
        unsigned int newscore =
            bestFoundry(script, score, request.styleStrategy,
                        test.family, foundry_name, styleKey, request.pixelSize, pitch,
                        &test, request.styleName);
......................