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

Verified 2026-10-292 min read

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

Tested onPro (26H2) / Server · Build 26300.9457 / 26100.33650 · x64

Build: 26300.9457 / 26100.33650
Edition: Pro (26H2) / Server
Architecture: x64
Support: Documentation (E1)
Evidence: E1Official documentation
Verified: 2026-10-29
Page type: Troubleshoot

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:

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.

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.

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, 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

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.

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.