add i18n support

[benedikt-bartscher]

closes #2339

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing benedikt-bartscher:add-i18n (c88fd65) with main (d932ee8)²}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (02f442b) during the generation of this report, so d932ee8 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[greptile-apps]

Greptile Summary

This PR adds reflex-i18n, a new first-party internationalization package for Reflex apps, and wires it into the core framework. It introduces client-side static translation (rx.t), server-side dynamic translation (gettext/ngettext/pgettext), locale-aware number/date formatting (Babel + Intl), and a reflex i18n CLI for catalog management.

• Core mechanism: A new _EventScope hook in reflex-base lets plugins inject per-event ambient context (here, the active locale ContextVar). The scope is entered both during handler execution and again during delta resolution so computed vars that call gettext recompute in the right locale after a set_locale call.
• Client runtime: An I18nProvider React component manages locale state via cookie and navigator.languages, loads per-locale catalog chunks lazily, and exposes useTranslation/useFormat/useLocale hooks. Catalog JS modules are emitted at compile time (tree-shaken to only used messages).
• Dependency tracking: A new implicit-dependency mechanism in dep_tracking.py makes computed vars that reference gettext automatically depend on I18nState.locale, so they recompute when the locale changes.

Confidence Score: 5/5

Safe to merge; no functional regressions identified in the new i18n subsystem or the core framework changes.

The previously flagged issues (context manager leak in _EventScope.aenter, RFC 7231 q=0 exclusion in negotiate_locale, unhandled catalog-load rejection in i18n.js, missing set_locale in the lazy-loader mapping, and add_command outside the try block in reflex.py) are all addressed in this version. The event-scope integration, implicit dependency tracking, and client-side catalog compilation are logically sound. The only remaining findings are minor style and structural observations that do not affect runtime behaviour.

Files Needing Attention: No files require special attention. reflex/i18n.py has a structural note about eager I18nState import, but the practical impact is minimal.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/event/processor/scope.py	New per-event ambient context hook. The mid-loop BaseException guard in __aenter__ correctly prevents contextvar leaks when a later provider raises.
packages/reflex-base/src/reflex_base/event/processor/base_state_processor.py	Wraps both handler execution and delta resolution in event_scope; background tasks get their own second scope after the lock is dropped. Flow is correct.
packages/reflex-i18n/src/reflex_i18n/runtime.py	Server-side gettext + Babel formatting. RFC 7231 q=0 exclusion, ContextVar locale management, lazy translation caching, and implicit dependency registration are all correctly implemented.
packages/reflex-i18n/src/reflex_i18n/state.py	I18nState with cookie-backed locale, locale negotiation, and event scope provider. The _locale_scope correctly re-reads the cookie for each event phase so a locale change by a handler is visible during delta resolution.
packages/reflex-i18n/src/reflex_i18n/_web/i18n.js	Client runtime: I18nProvider with cookie + navigator.languages locale negotiation. Promise rejection on catalog load is caught; Secure flag on cookie is conditioned on HTTPS. Race condition on rapid locale changes is handled via a cancelled flag.
packages/reflex-i18n/src/reflex_i18n/catalog.py	Compiles .po catalogs to JS modules. Plural expression is whitelist-validated before embedding. json.dumps used for all string values, preventing injection.
packages/reflex-i18n/src/reflex_i18n/vars.py	Implements rx.t() — requires literal strings at call time for catalog extraction; properly validates plural/count pairing.
packages/reflex-i18n/src/reflex_i18n/format.py	Client-side locale-aware number/date formatting vars using Intl API via useFormat hook. Formatter cache capped at 100 entries to prevent unbounded growth.
packages/reflex-i18n/src/reflex_i18n/plugin.py	I18nPlugin registers state and ships the JS runtime. Lazy state import in post_init avoids registering I18nState for apps that only load the CLI entry point.
reflex/init.py	Adds i18n lazy-loader mapping including set_locale and t; correct.
reflex/i18n.py	Re-exports all reflex_i18n public API. Eagerly imports I18nState (which registers it as a substate), meaning accessing any rx.* i18n attribute triggers state registration — partially defeating the lazy-load intent in reflex_i18n/init.py.
reflex/reflex.py	Plugin CLI command loading now validates that the resolved object is a click.Command before calling add_command, preventing a TypeError from aborting the whole CLI startup.
packages/reflex-base/src/reflex_base/vars/dep_tracking.py	Adds implicit dependency registration for LOAD_GLOBAL and LOAD_DEREF opcodes. Unhashable-object guard via try/except TypeError is correct.
reflex/state.py	Splits reload_state_module to also purge dangling dependency edges pointing at removed states, fixing a hot-reload crash in _mark_dirty_computed_vars.
packages/reflex-i18n/src/reflex_i18n/cli.py	Implements reflex i18n extract/init/check commands. Stats and merge logic are correct; check_command does not write to disk.

_{Reviews (10): Last reviewed commit: "Merge remote-tracking branch 'upstream/m..." | Re-trigger Greptile}

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remove development pins before publishing reflex-i18n

With the new dispatch-release option, selecting reflex-i18n will create a release and trigger .github/workflows/publish.yml, whose publish job runs scripts/check_min_deps.py --check-dev-pins "$PACKAGE" and explicitly rejects published dependencies containing *.dev pins. Because these two requirements are part of reflex-i18n's published metadata, the publish workflow for any reflex-i18n release will fail at that gate until they are pinned to released versions.

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[benedikt-bartscher]

I'll leave this open for the maintainers