# Fonts and CJK rendering: missing glyphs, blur and the font cache

> Why a document shows boxes, how to rebuild the font cache, and why ClearType and scaling fight each other.

**Tested on**

- Build: 26300.9457 / 26100.33650
- Edition: Pro (26H2) / Server
- Architecture: x64
- Evidence: E1
- Verified: 2026-10-29

## The short answer

Three different problems get called "font problems":

| Symptom | Cause |
|---|---|
| **Boxes / question marks** | the font lacks the glyphs (missing CJK font, or a subsetted PDF font) |
| **Blurry text** | DPI scaling on a non-DPI-aware app, or a bitmap font |
| **Wrong glyph shapes** | wrong font selected for the script (Japanese vs Chinese variants) |

They have different fixes. Installing "more fonts" only helps the first.

## Missing glyphs

Windows ships CJK support through optional features: **Settings → System → Optional features → Add a feature** → *Chinese (Simplified) Supplemental Fonts* (and the Traditional/Japanese/Korean equivalents).

Check what is installed:

```powershell
Get-WinUserLanguageList | Select-Object LanguageTag,InputMethodTips
Get-ChildItem C:\Windows\Fonts -Filter *.tt? | Measure-Object
# installed optional font packages
Get-WindowsCapability -Online -Name 'Language.Fonts.*' | Select-Object Name,State
```

If a **PDF** shows boxes while the same text is fine in a browser, the PDF embeds a subset that lacks those glyphs — a font problem in the document, not in Windows.

## Wrong CJK variants

The same Unicode codepoint renders differently depending on the font: Chinese (simplified) 直 vs Japanese 直 look subtly different. If a document looks "Japanese" while you typed Chinese, the font fallback picked a Japanese face.

Fix by setting the document/application font explicitly to a Chinese face (`Microsoft YaHei`, `SimSun`, `Noto Sans SC`) rather than relying on fallback.

## The font cache

Windows caches font data; a corrupt cache produces missing fonts, apps that cannot see a newly installed font, or a slow Settings app.

```powershell
Stop-Service FontCache
Remove-Item "$env:SystemRoot\ServiceProfiles\LocalService\AppData\Local\FontCache\*" -Force -ErrorAction SilentlyContinue
Start-Service FontCache
```

Reboot afterwards. The cache rebuilds itself — the first launch of font-heavy apps will be slower once.

> **Caution: Install fonts for all users, not just yourself**
>
> Right-click → **Install** puts a font in the per-user store; **Install for all users** puts it in `C:\Windows\Fonts`. Services and other accounts only see the latter — the usual reason "the font works in Word but not in a report generated by a service".

## Blurry text at scaling

ClearType was designed for 96 DPI. At 125–200% scaling:

- **DPI-aware apps** re-render at the new scale → sharp.
- **Non-aware apps** are bitmap-stretched → blurry.
- **Bitmap fonts** (old installers, some tools) cannot scale at all.

That is the same mechanism as [high DPI and scaling](https://windows.homes/en/hardware/display/dpi-scaling/), not a font defect.

Turning ClearType off makes text thinner but not sharper at high DPI; it is not a fix for a non-aware app.

## Verify a font actually resolves

```powershell
Add-Type -AssemblyName System.Drawing
$families = (New-Object System.Drawing.Text.InstalledFontCollection).Families
$families | Where-Object Name -match 'YaHei|SimSun|Noto' | Select-Object Name
```

If the family is absent, the application cannot use it regardless of the file being on disk.

## Related

- [High DPI and scaling](https://windows.homes/en/hardware/display/dpi-scaling/)
- [Colour management and ICC](https://windows.homes/en/windows/media/colour-management/)
- [Video codecs](https://windows.homes/en/windows/media/codecs/)

## Lab boundary

E1. Font and text rendering behaviour is documented by Microsoft. The lab VMs have CJK fonts installed by default, so no missing-glyph case was reproduced.

## Sources

- [Microsoft Learn — Fonts and text](https://learn.microsoft.com/en-us/windows/win32/gdi/fonts-and-text)
- [Microsoft Learn — Typography](https://learn.microsoft.com/en-us/typography/)
- [Microsoft Learn — High DPI desktop application development](https://learn.microsoft.com/en-us/windows/win32/hidpi/high-dpi-desktop-application-development-on-windows)

---

Source: https://windows.homes/en/windows/media/fonts-cjk/