Enable the language switcher and fix URLs copied from the English config

[mmcky]

Two related changes: enable the language switcher, and stop this edition advertising itself as the English site. The second is a prerequisite for the first to be worth anything, which is why they are together — see below.

1. Language switcher

Adds the switcher configuration to html_theme_options, mirroring QuantEcon/lecture-python-programming#490 which adds the same block to the English source.

Code	Name	URL
en	English	https://python-programming.quantecon.org
fa	فارسی	https://quantecon.github.io/lecture-python-programming.fa
fr	Français	https://quantecon.github.io/lecture-python-programming.fr
zh-cn	中文	https://quantecon.github.io/lecture-python-programming.zh-cn

current_language: zh-cn, so this edition renders as active. English stays first because the theme uses languages[0] as the hreflang x-default target.

This does not propagate from the English source: the sync workflows trigger only on lectures/**/*.md and lectures/_toc.yml, so _config.yml never reaches a sync run, and each edition needs its own current_language anyway.

2. URLs copied from the English config

Four settings appear to have been copied from the English _config.yml and never updated, with the effect that this edition presented itself as the English site:

Setting	Was	Effect
html.baseurl	the English site	every page emitted a canonical and og:url declaring it a duplicate of the English page
repository_url	the English repo	"View Source" sent Chinese readers and editors to the English repository
nb_repository_url	the English notebooks repo	notebook links pointed at English notebooks
tojupyter_urlpath / _image_urlpath	the English site	generated notebooks resolved their links and images against the English site

baseurl and the two tojupyter paths now use this edition's GitHub Pages address, which is where it is hosted while the broader URL structure is worked out. repository_url points here.

nb_repository_url is dropped rather than repointed: lecture-python-programming.zh-cn.notebooks does not exist. Replaced with the same explanatory comment the fr edition already carries; the theme omits notebook-launch links when the option is unset, which is how .fr runs in production today.

The canonical is the one that interacts with part 1. An hreflang cluster asserting the Chinese version lives here, on pages that simultaneously declare themselves the English page, is incoherent — search engines resolve it by preferring the canonical, so the annotations would have been discounted. Fixing the canonical is what makes the switcher's SEO half function.

Verification

Built locally against the theme:

• The switcher lists all four languages with 中文 active.
• hreflang alternates inject, including x-default → en.
• canonical and og:url now read https://quantecon.github.io/lecture-python-programming.zh-cn/{page}.html, matching this edition's own hreflang self-reference.

No environment change needed. This repo pins quantecon-book-theme==0.20.0, and I confirmed against the v0.20.0 tag that it already carries the languages/current_language options and the switcher and hreflang template code. Moving to 0.21.0 to match the other editions is worth doing separately.

Note

Nothing here changes a live page until a publish* tag is pushed. This edition last published on 2026-06-19.

[Copilot]

Pull request overview

Adds Quantecon Book Theme language-switcher configuration to the Chinese edition’s Sphinx theme options so the UI switcher (and theme-provided hreflang alternates) can be rendered correctly with 中文 marked active.

Changes:

• Add a languages list (en/fa/fr/zh-cn) under html_theme_options.
• Set current_language: zh-cn to activate the Chinese entry in the switcher.

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