[mmcky]

Part of #298. #302, the sync of QuantEcon/lecture-python.myst#1050, carried every English change into sir_model, but it also rewrote passages whose English did not change. The lecture carries a native review from 2025 (yuki, Humphrey Yang), and five of the twenty lines still attributed to that review were among the rewritten ones. This PR puts the reviewed text back where the English is unchanged and keeps every change the English made, in the manner of #304's var_dmd commit.

What changes

Where	#302's text	Restored	Why
时间路径	跨状态的流动遵循路径…	状态之间的流动遵循路径…	English unchanged
时间路径	我们主要关注以下几点：, then two reworded bullets	主要关注的是, then yuki's two bullets	English unchanged
时间路径	用小写字母表示每种状态下人口的比例，动态方程为	使用小写字母表示处于各状态的人口比例，其动态方程为	the English changed only "lower case" to "lowercase"
时间路径	在这些方程中：	在这些方程中，	English unchanged
时间路径	由于这些状态构成了一个划分，…处于 R 状态…	我们不需要单独建模处于 $R$ 状态的人口比例 $r$，因为这些状态构成一个分区。	English unchanged; R is math again
时间路径	具体而言，人口中“已移除”的比例为…	具体来说，“已移除”的人口比例为…	English unchanged
时间路径	…即累计病例数（即所有曾经或正在感染的人）。	…即累计病例数（即所有已感染或曾经感染的人）。	English unchanged
参数	three reworded lines, one with 阿特克森	the three reviewed lines, with Atkeson	English unchanged; the lecture writes Atkeson everywhere else
参数	（这个符号稍显混乱，…表示移除状态…）	（这个符号表示有点令人困惑，…表示已移除状态…）	English unchanged
SEIR 模型	易感（$S$）、暴露（$E$）、感染（$I$）和移除（$R$）	易感者（$S$）、暴露者（$E$）、感染者（$I$）和移出者（$R$）	the intro's reviewed state names, with the English's new $S$, $E$, $I$, $R$
code	set_xlabel('days') twice, ylabel='fraction of the population' four times	'天数', '人口比例'	解除封锁 already used 人口比例, and the lecture loads the Chinese font

Where the restored text had ASCII quotes or parentheses, they are now full-width, as the zh-cn rules require.

What keeps #302's text

• Every change the English made: the SEIR rename, the assumption block, the calibration paragraphs, odeint in code font, the reworded captions, and the code.
• Lines from the July forward resync ([action-translation] resync: sir_model.md #151) that 🌐 [translation-sync] [sir_model] update code and text #302 then reworded. No reviewer saw them, so they stay as 🌐 [translation-sync] [sir_model] update code and text #302 wrote them, except the state list, which now matches the intro.
• Lines where 🌐 [translation-sync] [sir_model] update code and text #302 kept the reviewed wording and changed only spacing, such as the {eq}dfcv sentence.

Checks

• Structure: structural parity against lecture-python.myst main holds under the engine's guard at QuantEcon/action-translation f89f061. The 25 code cells match the source with string literals and comments masked; the only difference is this edition's font block. Both math blocks are byte-identical.
• Restored text: every restored line is byte-identical to the text before 🌐 [translation-sync] [sir_model] update code and text #302, apart from full-width punctuation and the English's new math in the state list.
• zh-cn rules (QuantEcon/project-translation#70): full-width punctuation, and a space between Chinese and an inline role or link, hold on every prose line. The text before 🌐 [translation-sync] [sir_model] update code and text #302 had 17 findings; main and this branch have none.
• State: translate status still reads sir_model as ALIGNED. The state file is unchanged, because the source is.
• Preview: the preview build executed sir_model in 2.85 s. Its log has no Executing notebook failed (The -W gate is blind in ci.yml, and a warning-only cache failure discards a completed execution #271), no traceback and no missing-glyph warning, and the HTML build succeeded.

The branch is a recover/ branch, so the rebase automation neither triggers on it nor rebases it, as with #300 and #301.

Not in this PR: the July forward resync (#151) had already dropped 26 of the reviewers' 47 lines in this lecture, before #302. Whether to restore those belongs with the audit of forward-written text (QuantEcon/action-translation#154), not with this repair.

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🟢 Approval recommended

The changes are low-risk prose restorations and string-label localizations with no code-logic or structural changes, and verified consistency in labels, state names, terminology, and font loading.

No open issues 🎉

What changed in this PR

This PR repairs lectures/sir_model.md, part of the #298 recovery effort. The prior automated sync (#302) correctly carried every English change but also rewrote five Chinese passages whose English was unchanged, discarding wording from the lecture's native 2025 review (yuki, Humphrey Yang). This PR restores the reviewed text wherever the English did not change, preserves every change the English did make, and resolves two consistency defects (bilingual plot labels and mismatched state names), bringing the Chinese edition back in line with its reviewed state while staying structurally aligned to the source.

Changes:

• Restore reviewer wording in the 时间路径 and 参数 subsections (bullets, equation lead-ins, the $R(t)$-vs-$R$ note, and Atkeson instead of 阿特克森), with ASCII punctuation converted to full-width.
• Align the SEIR state list (line 84) with the intro's reviewed names (易感者…移出者) while keeping the English's new $S$, $E$, $I$, $R$ math.
• Localize remaining English plot labels to Chinese ('days'→'天数', 'fraction of the population'→'人口比例').

File	Description
lectures/​sir_model.md	Restores 2025 reviewer wording where English is unchanged, aligns state names with the intro, and localizes the remaining English plot labels to Chinese.

_{Review effort: Balanced}

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