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name: frontend-i18n description: Add, change, or review user-facing text in the Langflow frontend using the i18n system (i18next / react-i18next). Use whenever a change adds or edits UI strings — labels, buttons, tooltips, modals, toasts, error messages, empty states — or when reviewing a diff that contains user-facing text. Every user-facing string must go through the translation system and every new key must exist in ALL locale files. Do NOT use for backend strings, log messages, or code identifiers.

Frontend i18n

The Langflow frontend is internationalized with i18next + react-i18next. Locales live in src/frontend/src/locales/ — currently en, de, es, fr, ja, pt, zh-Hans. A hardcoded user-facing string, or a key missing from one locale, ships broken UI for part of the user base.

The two rules

1. Every user-facing string goes through t(...) — never hardcoded JSX text for labels, buttons, tooltips, modals, toasts, errors, placeholders, aria-labels, or empty states.
2. Every new key is added to ALL locale files in the same PR (en.json, de.json, es.json, fr.json, ja.json, pt.json, zh-Hans.json). fallbackLng: "en" means a missing key silently shows English — it won't crash, which is exactly why reviews must catch it.

How it works here

• Config: src/frontend/src/i18n.ts — a custom i18next instance. en is bundled statically; other languages are lazy-loaded by loadLanguage() via dynamic import. Language preference comes from localStorage.getItem("languagePreference"), normalized (e.g. zh-CN → zh-Hans, unknown → en).
• Keys are flat, dot-namespaced by feature: deleteModal.title, errors.fileTooLarge, crash.restartButton. Follow the existing namespace of the area you're touching; create a new prefix only for a genuinely new surface.
• Interpolation uses {{variable}} in the string and an options object in the call.

Adding a string (the pattern)

import { useTranslation } from "react-i18next";

const { t } = useTranslation();

<span>{t("deleteModal.title")}</span>
<p>{t("errors.fileTooLarge", { maxSizeMB: "10MB" })}</p>

In locales/en.json (and every other locale file):

"errors.fileTooLarge": "The file size is too large. Please select a file smaller than {{maxSizeMB}}."

For the non-English locales, write a real translation when confident; if not, add the key with the English value and flag it in the PR — a present-but-untranslated key is visible and searchable, a missing key is invisible.

Rules that prevent real bugs

• Don't concatenate translated fragments (t("a") + name + t("b")) — word order differs across languages. Use one key with interpolation: t("greeting", { name }).
• Don't put JSX/HTML inside translation strings; compose in JSX around t() calls (see how crash.descriptionBefore / crash.githubIssues / crash.descriptionAfter split around a link).
• Plurals: use i18next plural forms (_one / _other suffixes), not count === 1 ? ... : ....
• Keys are code: renaming or deleting a key means updating all seven locale files — an orphan key in one file is dead weight; a rename missed in one file is a regression.
• Dates/numbers/currency: format with Intl.* using the active locale, never hardcoded formats.

Review checklist (apply to any diff with UI text)

• [ ] No hardcoded user-facing string in JSX (including placeholder, title, aria-label, toast/error text).
• [ ] Every new key exists in all locale files (grep the key across src/frontend/src/locales/*.json).
• [ ] No concatenation of translated fragments; interpolation used instead.
• [ ] Removed/renamed keys cleaned up in all locales (no orphans).
• [ ] Key follows the existing dot-namespace of the feature area.

Quick check for a key across locales:

for f in src/frontend/src/locales/*.json; do grep -L '"my.new.key"' "$f"; done

(prints the locale files where the key is missing — should print nothing)