[Bug]: Code blocks render Vietnamese (non-Latin) diacritics poorly — no font override option

[dungphan0038]

Bug Description

In code blocks, Vietnamese characters with diacritics (ư, ơ, đ, ắ, ễ, ỗ, ự, ấ, ờ, ỹ, …) do not render in the monospace font. They fall back to a system font (e.g. Segoe UI), so the text looks misaligned/“broken” inside otherwise-monospaced code. There is no user-facing setting (Custom CSS or font picker) to override the code font, so non-Latin users cannot fix this without patching the app binary.

Steps to Reproduce

1. In the desktop app, set the theme to mono (or ember).

2. Send a message containing a code block with Vietnamese diacritics, e.g.:

   x = "học sinh mất gốc toán đà lạt — ưỡm ơ đễ"
   

3. Open DevTools (Ctrl+Shift+I) → Elements → inspect a <code>/<pre> element → look at computed font-family.

Expected Behavior

Diacritics render cleanly inside the monospace font, aligned with the rest of the code.

Actual Behavior

Computed font-family on the code element is e.g.:

"Courier Prime", "Cascadia Code", "JetBrains Mono", "SF Mono", ui-monospace, Menlo, Monaco, Consolas, monospace, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji", emoji

The theme’s primary mono font (Courier Prime, loaded via fontUrl: https://fonts.googleapis.com/css2?family=Courier+Prime...) does not contain Vietnamese glyphs, so diacritics fall through to a system font and render outside the monospace metrics.

Affected Component

Other

Messaging Platform (if gateway-related)

No response

Debug Report

Report       https://paste.rs/JwrO4
agent.log    https://paste.rs/iyXnD
gui.log      https://paste.rs/2ByPl
desktop.log  https://paste.rs/ij8yV

Operating System

Windows 11

Python Version

3.14.4

Hermes Version

0.18.2

Additional Logs / Traceback (optional)

Root Cause Analysis (optional)

Root cause (verified)

• Themes define typography.fontMono with a hardcoded stack; some themes pull the first font from Google Fonts over the network (Courier Prime, IBM Plex Mono). Those webfonts lack Vietnamese (Latin Extended-A) coverage.
• The font stack has no Vietnam/Latin-Extended-capable fallback mono font, so glyphs drop to a proportional system font.
• There is no settings/UI hook (verified: no customCss/injectCSS user path in the bundle; config.yaml has no font field) for the user to supply their own code font.
• Note: the app’s bundled JetBrains Mono woff2 does contain Vietnamese glyphs (confirmed via fontTools), so the default/nous theme is less affected — but any theme using Courier Prime / IBM Plex Mono shows the problem, and no theme lets the user choose a Vietnam-friendly font.

Impact

• Affects all non-Latin / diacritic-using users (Vietnamese, Thai, Arabic, CJK-mixed, etc.), not just Vietnamese.
• Degrades readability of exactly the content these users paste most (code with localized comments, math, notes).

Proposed Fix (optional)

Workaround (user-side, fragile)

Patching resources/app.asar → editing the bundled CSS to add an @font-face + code,pre{font-family:"X",monospace!important} (with a Vietnam-capable font such as Iosevka) and repacking works. Confirmed fix. But it is wiped on every auto-update, so it must be re-applied each release.

Suggested fixes (any one would resolve it)

1. Add a Vietnam/Latin-Extended-capable mono font to the fallback stack (e.g. Iosevka, or a system ui-monospace that covers the locale) after the primary theme font, so diacritics stay monospaced.
2. Ensure theme webfonts include Vietnamese subsets (request &subset=vietnamese from Google Fonts, or self-host a Vietnam-capable build).
3. Expose a user setting for the code font — either a “Code font” picker in Settings/Appearance, or a Custom CSS field — so users can supply their own font without binary patching.

Are you willing to submit a PR for this?

• I'd like to fix this myself and submit a PR

[GottZ]

This was generated by AI during triage.

Summary

Of the four triaged PRs, #61399 and #61401 directly address #61392 by changing monospace fallback stacks, while #39165 and #40989 only add the unrelated Hepburn theme and retain Courier Prime as its primary code font. #61399 is the strongest focused fix, although one out-of-scope typography change must be removed before merge; #61401 places its proposed fallback too late to be effective.

Related pull requests

• Add the Hepburn Theme for Hermes Desktop. #39165 [closed] unrelated — (+93/-2) — unrelated: Adds the Hepburn desktop theme and explicitly uses Courier Prime for code, but does not improve Vietnamese glyph fallback or add a font override. Although closed, it remains relevant as the earlier version superseded by the clean Hepburn-theme PR feat(desktop): add Hepburn theme #40989, not as a fix for [Bug]: Code blocks render Vietnamese (non-Latin) diacritics poorly — no font override option #61392.
• feat(desktop): add Hepburn theme #40989 unrelated — (+93/-2) — unrelated: Recreates Add the Hepburn Theme for Hermes Desktop. #39165's Hepburn theme addition with effectively the same palette, registration, tests, and Courier Prime typography; it does not address the reported missing-glyph fallback path.
• fix(desktop): preserve mono fallback for Latin Extended code #61399 best fix — (+50/-7) — best partial fix: Moves bundled JetBrains Mono and several Latin Extended-capable monospace faces ahead of generic fallbacks in the desktop theme and CSS stacks, with focused regression tests. The keep_open review on fix(desktop): preserve mono fallback for Latin Extended code #61399 is valid and must be addressed before merge: restore cyberpunk fontSans to its existing text stack, because appending SYSTEM_MONO there changes ordinary UI-text fallback outside the issue's code-font scope.
• fix(desktop): add Noto Sans Mono to monospace font stack for Vietnamese/non-Latin script support #61401 [closed] partial — (+24/-5) — ineffective partial fix: Adds and loads Noto Sans Mono, but places it after ui-monospace/monospace, so those generic families resolve first; its dashboard changes also do not load the named font. Despite the keep_open review on fix(desktop): add Noto Sans Mono to monospace font stack for Vietnamese/non-Latin script support #61401, keeping it closed is appropriate because the diff still contains exactly those blocking ordering and loading defects, and the contributor closure records it as stale; fix(desktop): preserve mono fallback for Latin Extended code #61399 provides the cleaner salvage path.

Duplicates

#39165 and #40989 are effectively duplicate Hepburn-theme changes; #39165 was closed and superseded by the clean draft #40989. They are not duplicates of the #61392 font-fallback fixes.

Suggested consolidation

Merge #61399 after applying its contributor-requested correction to keep cyberpunk fontSans unchanged and validating Vietnamese rendering through the primary desktop code-block path. Keep #61401 closed as superseded by #61399 because its fallback ordering is ineffective and its dashboard font loading is incomplete; do not close #40989 as a duplicate of this bug fix, since it is an unrelated theme feature, while #39165 is already closed as its superseded duplicate.

Complex graph

flowchart LR
    classDef open fill:#dbeafe,stroke:#1d4ed8,color:#1e3a8a
    classDef merged fill:#dcfce7,stroke:#15803d,color:#14532d
    classDef closed fill:#e5e7eb,stroke:#6b7280,color:#1f2937
    classDef unverified fill:#f3f4f6,stroke:#9ca3af,color:#374151
    classDef best stroke-width:3px,stroke:#b45309
    classDef target stroke-width:3px,stroke:#4338ca
    I61392(["issue #61392 (open)"])
    P61399["PR #61399 (open)"]
    P61401["PR #61401 (closed)"]
    subgraph Dup39165 ["PRs duplicating each other"]
        P39165["PR #39165 (closed)"]
        P40989["PR #40989 (open)"]
    end
    P61399 -->|best fix| I61392
    P61401 -.->|partial| I61392
    class I61392 open
    class I61392 target
    class P39165 closed
    class P40989 open
    class P61399 open
    class P61401 closed
    class P61399 best
    click I61392 "https://github.com/NousResearch/hermes-agent/issues/61392"
    click P39165 "https://github.com/NousResearch/hermes-agent/pull/39165"
    click P40989 "https://github.com/NousResearch/hermes-agent/pull/40989"
    click P61399 "https://github.com/NousResearch/hermes-agent/pull/61399"
    click P61401 "https://github.com/NousResearch/hermes-agent/pull/61401"

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Graph: solid arrow = fixes / best fix, dashed arrow = partial or unverified (see edge label); boxed group = PRs duplicating each other; amber border = best fix; indigo border = target; gray node = closed or no verify verdict yet (state tag in the node label).

Cross-PR triage: Reviewed 4 pull requests and 1 issue in this complex. Each diff was read against this issue; Assessment working set: 18 kB of PR diffs, 13 kB of issue/PR text, 4 kB of discussion (7 comments), 6 verify verdicts. verdicts reflect diff content, not PR titles. Part of an automated triage batch.