Fail to load large font

[trlsmax]

I try to load large font to display chinese char, but most of time it fail and display random wrong char.
here is how I load font:

        auto& io = ImGui::GetIO();
        ImFontConfig fontcfg;
        fontcfg.OversampleH = 4;
        fontcfg.OversampleV = 4;
        fontcfg.SizePixels = std::round(16 * screen_scalex);
        #ifdef _WIN32
        if (std::filesystem::is_regular_file("C:\\Windows\\Fonts\\simsun.ttc")) {
            ImFontGlyphRangesBuilder builder;
            ImVector<ImWchar> ranges;
            builder.AddText(u8"阈矢轴滞浏廓拷°²³√");
            builder.AddRanges(io.Fonts->GetGlyphRangesChineseSimplifiedCommon());
            builder.BuildRanges(&ranges);
            io.Fonts->AddFontFromFileTTF("C:\\Windows\\Fonts\\simsun.ttc", 20, &fontcfg, ranges.Data);
        } else {
			io.Fonts->AddFontDefault(&fontcfg);
        }
        #else
			io.Fonts->AddFontDefault(&fontcfg);
        #endif
        io.Fonts->Build();