`lang: zh-Hant` falls back to Simplified UI strings instead of Traditional

[cderv]

Quarto's subtag-prefix resolution splits lang on - and loads most-general-first:

quarto-cli/src/core/language.ts

Lines 56 to 133 in e4b75c1

	export async function readLanguageTranslations(
	translationFile: string,
	lang?: string,
	): Promise<{ language: FormatLanguage; files: string[] }> {
	// read and parse yaml if it exists (track files read)
	const files: string[] = [];
	// read the original file
	const {
	file,
	language,
	} = await translationCache(translationFile);
	if (file) {
	files.push(file);
	}
	// determine additional variations to read
	const ext = extname(translationFile);
	let [dir, stem] = dirAndStem(translationFile);
	stem = escapeRegExp(stem);
	const variations: string[] = [];
	if (lang) {
	// enumerate variations dictated by this lang
	const subtags = lang.split("-");
	for (let i = 0; i < subtags.length; i++) {
	variations.push(subtags.slice(0, i + 1).join("-"));
	}
	} else {
	// enumerate all variations
	const glob = stem + "-*" + ext;
	const variationRe = new RegExp(
	"^" + stem + "-(.*?)" + ext,
	);
	for (
	const entry of expandGlobSync(glob, {
	root: dir,
	includeDirs: false,
	caseInsensitive: true,
	})
	) {
	const match = entry.name.match(variationRe);
	if (match) {
	variations.push(match[1]);
	}
	}
	}
	// read the variations
	for (const variation of variations) {
	const {
	file: variationFile,
	language: translations,
	} = await translationCache(join(dir, stem + "-" + variation + ext));
	if (variationFile) {
	files.push(variationFile);
	}
	// const translations = await maybeReadYaml(
	// join(dir, stem + "-" + variation + ext),
	// );
	Object.keys(translations).forEach((key) => {
	// top level entries use the variation key
	if (kLanguageDefaultsKeys.includes(key)) {
	language[variation] = language[variation] || {};
	(language[variation] as FormatLanguage)[key] = translations[key];
	// objects use variation key + subkey
	} else if (typeof translations[key] === "object") {
	const targetKey = variation + "-" + key;
	language[targetKey] = language[targetKey] || {};
	language[targetKey] = {
	...language[targetKey] as Record<string, unknown>,
	...translations[key] as Record<string, unknown>,
	};
	}
	});
	}
	return { language, files };
	}

For lang: zh-Hant this loads _language-zh.yml (Simplified) and then looks for _language-zh-Hant.yml (doesn't exist). Result: Traditional-script readers get Simplified UI strings — wrong script.

Quarto's _language-zh-TW.yml is Traditional in script but uses Taiwan-specific vocabulary (added deliberately in #6512 — OpenCC script conversion followed by manual region-specific corrections). A generic zh-Hant file does not exist.

Design question

How should lang: zh-Hant resolve?

• (a) Fallback rule: if _language-zh-Hant.yml doesn't exist, try _language-zh-TW.yml. Taiwan vocabulary is closer to HK/MO than Simplified is, and this matches Pandoc's posture of shipping one generic zh-Hant file. Could be documented as best-effort until a proper generic file exists.
• (b) Wait for a contributed generic _language-zh-Hant.yml.
• (c) Add _language-zh-Hant.yml as a copy of the TW file. Behaviorally equivalent to (a) but less honest about regional scope.

Repro

---
lang: zh-Hant
format: html
---

Inspect generated UI strings (TOC title, "Copy to clipboard" tooltip, section titles in HTML article). They render in Simplified Chinese.

From #14409. Related: #14416.