refactor(i18n)!: adopt the shared i18n layer from stream-chat/i18n (#3271)

Adopts the shared i18n layer from `stream-chat/i18n`, deleting ~1,100
lines of runtime this package no longer needs to own: `Streami18n`, the
formatter/date half of `i18n/utils.ts`,
`TranslationBuilder/TranslationBuilder.ts`, `externalStrings.ts`, and
most of the codegen script (249 lines → ~40, over the generator core now
ships).

What stays here is what is genuinely this SDK's: the generated key
catalog, `runtimeDefaults`, and the notification translation topic.

**Behaviour changes**

- Notification copy is a `Record<CoreNotificationType, Translator>`, so
a new identifier in `stream-chat` is a compile error until mapped. Dead
rows for identifiers this SDK never emits are gone; three
previously-unmapped core identifiers now translate instead of rendering
untranslated English.
- The 57 `language.*` entries move to core, generated from
`TranslationLanguage`, so `MessageTranslationIndicator` drops its
`asDynamicKey` + string-compare miss detection.
- Reactivity is core's `StateStore`. `setLanguage()` returns `void`;
`getTranslators()` is now `init()`. **No deprecated aliases** —
`Streami18n` keeps its name, so integrator code is unchanged there.
- Two timestamp edge cases render differently; both documented in
`ai-docs/i18n-v15-migration.md`.
- Drops `i18next` / `dayjs` / `moment-timezone` from `dependencies` —
core supplies the first two, and the third's type leak into the
published `.d.ts` is replaced by core's structural `DateTimeLike`.

Also adds a `catalogRenders` test (this package had no equivalent of
RN's regression net) and puts `release-v15` in `size.yml`'s branch
filter, which was only running on `master`.

**Verified** against a locally packed core: 2,829 tests, `validate-esm`,
`validate-cjs`, lint. Adopting the shared layer surfaced seven real
defects in it, all fixed in the core PR with regression tests.

⚠️ **Blocked:** needs `stream-chat@10.0.0-rc.3`
(GetStream/stream-chat-js#1830). The lockfile is deliberately untouched
and must be regenerated once that publishes — until then `yarn install
--immutable` fails, hence draft.

Pre-existing and not from this PR: `yarn build`'s `tsc` step fails on 3
imports (`APIErrorResponse`, `EventAPIResponse`) removed from core after
rc.2. Needs fixing when this package bumps its core range.

Author: oliverlaz

.github/workflows/size.yml

@@ -4,6 +4,10 @@ on:
   pull_request:
     branches:
       - master
+      # The v15 release branch. Without it this workflow does not run on any PR stacked onto it, so the
+      # i18n consolidation's central size claim -- that moving the runtime into `stream-chat/i18n`
+      # shrinks the root bundle -- goes unmeasured for the whole release.
+      - release-v15
     paths-ignore:
       - '**.test.*'
       - '**.md'

ai-docs/i18n-v15-migration.md

@@ -1,26 +1,32 @@
 # i18n changes in v15
 
-Two breaking changes, both in v15:
+Three breaking changes, all in v15:
 
 1. **English is the only bundled language.** The `de`, `es`, `fr`, `hi`, `it`, `ja`, `ko`, `nl`,
    `pt`, `ru` and `tr` dictionaries are gone, along with their `dayjs` locale data.
 2. **Translation keys are namespaced identifiers**, not the English text. `t('Send Message')`
    became `t('messageComposer.sendButton.send.ariaLabel', 'Send')`.
+3. **The translation runtime moved into `stream-chat`**, shared with the React Native SDK. The class
+   keeps its name, two of its methods changed shape, and two timestamp edge cases render differently
+   — see [The shared runtime](#the-shared-runtime).
 
 Together these cut ~112 KB gzip (27%) from the bundle: the 11 dictionaries were statically
 imported and copied into `Streami18n` at construction, so they shipped even if you never set
 `language`.
 
 ## Do I need to do anything?
 
-| If you…                                       | Action                                         |
-| --------------------------------------------- | ---------------------------------------------- |
-| use the SDK in English and never touched i18n | **Nothing.**                                   |
-| passed `translationsForLanguage`              | Rename your keys — see below                   |
-| called `registerTranslation()`                | Rename your keys — see below                   |
-| used a built-in non-English language          | Supply the dictionary yourself — see below     |
-| relied on non-English date formats            | Import the `dayjs` locale yourself — see below |
-| imported `deTranslations` … `trTranslations`  | Those exports are removed                      |
+| If you…                                          | Action                                         |
+| ------------------------------------------------ | ---------------------------------------------- |
+| use the SDK in English and never touched i18n    | **Nothing.**                                   |
+| passed `translationsForLanguage`                 | Rename your keys — see below                   |
+| called `registerTranslation()`                   | Rename your keys — see below                   |
+| used a built-in non-English language             | Supply the dictionary yourself — see below     |
+| relied on non-English date formats               | Import the `dayjs` locale yourself — see below |
+| imported `deTranslations` … `trTranslations`     | Those exports are removed                      |
+| construct `new Streami18n(...)`                  | **Nothing** — same name, same options object   |
+| assign `i18n.t` or read `setLanguage()`'s return | Both changed — see below                       |
+| declared `i18next` or `dayjs` yourself           | You can drop them; `stream-chat` supplies both |
 
 ## Renaming your keys
 
@@ -191,10 +197,19 @@ export const de = {
   'common.back.label': 'Zurück',
 } as const satisfies TranslationDictionary;
 
+/** Formatter keys hold `dayjs` / `i18next` expressions, not copy, so they are not "translated". */
+type TranslatableKey = Exclude<
+  keyof TranslationCatalog,
+  `duration.${string}` | `timestamp.${string}` | `translationBuilderTopic.${string}`
+>;
+
 /** Every key still needing German. Hover it to read the list. */
-type Untranslated = Exclude<keyof TranslationCatalog, keyof typeof de>;
+type Untranslated = Exclude<TranslatableKey, keyof typeof de>;
 ```
 
+`language.*` (ISO language names) and `relativeTime.*` are ordinary copy and stay in the diff — they
+render in the UI like anything else, so a complete language translates them too.
+
 Hovering `Untranslated` in your editor lists the missing keys, and it shrinks as you add them. To
 turn "am I complete?" into a build failure — useful in CI after a dependency bump — assert the diff
 is empty:
@@ -228,6 +243,139 @@ git show v14.11.0:src/i18n/de.json > de.json
 Then rename its keys with the mapping table above and register it. Note the old file's keys are the
 _old_ natural-language keys, so it needs the same rename as your own overrides.
 
+## The shared runtime
+
+`Streami18n` used to live in this package. It now lives in `stream-chat` and is shared with
+`stream-chat-react-native`, so both SDKs behave identically and a fix reaches both at once. You still
+import it from here, and it still carries this SDK's own key catalog and copy.
+
+### `getTranslators()` is now `init()`
+
+Same return value; the old name was a getter that initialized, which is what made it worth renaming.
+
+```ts
+// v14
+const { t, tDateTimeParser } = await i18n.getTranslators();
+
+// v15
+const { t, tDateTimeParser } = await i18n.init();
+```
+
+`init()` is idempotent and safe to call concurrently — the promise is memoized, which closes a
+re-entry window the old implementation left open.
+
+### `t` is read-only, and `setLanguage()` returns nothing
+
+`t` is published through a reactive store rather than being a mutable field, which is what lets
+`<Chat>` pick up a language change without remounting. Two consequences:
+
+```ts
+// v14 — assigning `t` directly
+(i18n as any).t = myTranslator;
+
+// v15 — publish it, and every subscriber updates
+i18n.overrideTFunction(myTranslator);
+```
+
+```ts
+// v14 — setLanguage returned a translator (sometimes; it had three return shapes)
+const t = await i18n.setLanguage('de');
+
+// v15 — it returns void. Read the current `t` from the instance, or let <Chat> re-render.
+await i18n.setLanguage('de');
+const { t } = i18n.state.getLatestValue();
+```
+
+The returned translator was removed deliberately: it went stale on the next language change, so
+holding onto it was always a latent bug.
+
+### `getTranslations()` and `getAvailableLanguages()` are gone
+
+Both were public in v14, both leaked internal bookkeeping, and neither had a consumer in this SDK.
+
+```ts
+// v14 — reading the raw i18next resource map
+i18n.getTranslations().en.translation['some.key'];
+
+// v15 — render the key instead; that is the thing you actually wanted to know
+i18n.t('some.key');
+```
+
+`getTranslations()` never held this SDK's English copy in the first place: prose renders from the
+inline `defaultValue` at each call site, so the resource map only ever contained the bundled formatter
+expressions plus whatever had been registered.
+
+```ts
+// v14 — "available" included languages created only to carry the bundled defaults,
+// so a language nobody registered showed up here
+i18n.getAvailableLanguages().includes('de');
+
+// v15
+i18n.registeredLanguages.has('de');
+```
+
+`registeredLanguages` is now a `ReadonlySet<string>`. Reading it is unchanged; `.add()` no longer
+compiles — use `registerTranslation()`, since adding to the set would claim a language is registered
+with no dictionary behind it.
+
+Also now internal, none of them documented before: `translations`, `dayjsLocales`,
+`isCustomDateTimeParser`, `localeExists()`, `addOrUpdateLocale()`, `validateCurrentLanguage()`. To
+register a dayjs locale directly, `stream-chat/i18n` exports `addOrUpdateDayjsLocale()`.
+
+### `useChat` no longer returns `translators`
+
+The i18n wiring moved out of `useChat` into a dedicated `useStreami18n`, matching the hook
+`stream-chat-react-native` already had. `useChat` was doing five unrelated jobs — user-agent stamping,
+subsystem subscriptions, mutes, i18n and latest-message bookkeeping — and only held the translators to
+hand them straight to a provider.
+
+`useChat` is exported, so if you called it directly:
+
+```ts
+// v14
+const { translators } = useChat({ client, defaultLanguage, i18nInstance });
+
+// v15
+const { getAppSettings, latestMessageDatesByChannels, mutes } = useChat({ client });
+const translators = useStreami18n({ client, i18nInstance });
+```
+
+`useChat` no longer takes `i18nInstance`, which moved to `useStreami18n`. `defaultLanguage` is gone
+from both, and from `<Chat>` — see below.
+
+### `defaultLanguage` is removed, and so is browser detection
+
+`<Chat defaultLanguage>` read as a fallback for UI translations, but it never drove them: the
+`Streami18n` instance does. All it fed was `userLanguage`, which is the key the SDK reads
+`message.i18n[<lang>_text]` with — and a fallback there cannot help, because with no
+`client.user.language` the API is not translating at all, so `message.i18n` is absent and the text
+falls through to `message.text` regardless.
+
+For the same reason `userLanguage` no longer falls back to the two-letter browser language when that
+language happens to have a registered dictionary. Having German UI copy says nothing about whether the
+API produces `message.i18n.de_text`, so that branch only ever produced lookups that missed.
+`stream-chat-react-native` never had it.
+
+`userLanguage` is now `client.user.language` and nothing else, which is what every one of its consumers
+already assumed. A non-English UI comes from registering a dictionary and setting `language` on the
+instance; translated messages come from `language` in `connectUser`. The two are independent.
+
+One behavioural improvement comes with it. `userLanguage` tracks `client.user.language` reactively, so
+a language changed after connect now reaches the message components — it used to be read as a `useMemo`
+dependency with no subscription, so it only refreshed if something else re-rendered. Passing a value
+that is not a `Streami18n` warns and falls back to a default instance rather than throwing at render.
+
+### You no longer need `i18next` or `dayjs` in your own dependencies
+
+`stream-chat` depends on both, so they arrive transitively. If you declared them only for this SDK,
+remove them — and if you keep them, **match `stream-chat`'s ranges**. Two copies of `dayjs` means
+your `import 'dayjs/locale/de'` registers the locale on a different instance than the one formatting
+dates, and dates silently stay English:
+
+```bash
+find . -maxdepth 4 -name dayjs -type d -path '*node_modules*'   # expect exactly one
+```
+
 ## Date and time
 
 Only the `en` dayjs locale is bundled, and the per-language `calendar` formats the SDK used to ship
@@ -253,6 +401,46 @@ const i18n = new Streami18n({
 
 Or pass your own preconfigured `DateTimeParser` (dayjs or moment).
 
+### Two edge cases render differently
+
+Both are confined to a `timestamp.*` key that specifies **no** format. Every key the SDK ships
+specifies one (`format: HH:mm`, `calendar: true`, and so on), so you only see these if you overrode a
+timestamp key with an expression that formats nothing.
+
+**A `null` or unparseable timestamp renders as empty**, where v14 rendered the value stringified —
+which for `null` was the literal text `null`:
+
+```ts
+// a key with no format
+'timestamp.MessageTimestamp': '{{ timestamp | timestampFormatter(calendar: false) }}'
+
+// t('timestamp.MessageTimestamp', { timestamp: null })
+// v14 →  "null"
+// v15 →  ""
+```
+
+The same applies when you call `predefinedFormatters.timestampFormatter` yourself: it returns `''`
+rather than the stringified value. If you relied on that to spot a missing timestamp during
+development, check for the empty string instead — rendering the word `null` into a message list was
+never intentional.
+
+Note this is specifically about a value that _reaches_ the formatter. Passing no `timestamp` at all
+leaves i18next with nothing to interpolate, so the raw expression comes through unchanged — that was
+true in v14 too, and is a sign the option name is misspelled at the call site.
+
+**Unformatted output carries a numeric offset rather than `Z`:**
+
+```ts
+// v14 →  2019-04-03T14:42:47Z
+// v15 →  2019-04-03T14:42:47+00:00
+```
+
+Same instant, different ISO spelling. v14 called dayjs's `.tz()` on every parse even when no
+`timezone` was configured, which marks the instance as zoned and changes how `.format()` with no
+template renders. v15 applies `.tz()` only when you actually set `timezone`, matching what the React
+Native SDK already did. Configure a `format` on the key if you need a specific shape — relying on
+dayjs's default is fragile either way.
+
 ## Why keys changed at all
 
 The old keys _were_ the English copy, which meant:
@@ -266,8 +454,20 @@ Keys are now stable, and the English copy travels inline at the call site as i18
 `defaultValue`. That keeps the copy readable where it is used, and means a key you do not supply
 still renders English rather than a raw key path.
 
-The exception is the ~71 keys that carry no inline copy — `timestamp.*` and `duration.*` (formatter
-expressions), `language.*` (built from a runtime language code), and the postProcessor directive.
-Those are bundled in `runtimeDefaults` instead, and both `registerTranslation()` and
-`translationsForLanguage` merge your dictionary over them, so you inherit the working defaults
-without listing them. You only need to supply one if you want a different date format.
+The exception is the 15 keys that carry no inline copy — `timestamp.*` and `duration.*` (formatter
+expressions) and the postProcessor directive. Those are bundled in `runtimeDefaults` instead, and both
+`registerTranslation()` and `translationsForLanguage` merge your dictionary over them, so you inherit
+the working defaults without listing them. You only need to supply one if you want a different date
+format.
+
+Two more sets are still overridable but now come from `stream-chat`, because it owns the code that
+renders them:
+
+- **`language.*`** — the 57 language names used to say "Translated from German" on an auto-translated
+  message. They are derived from the same language union the API uses, so the set can no longer drift
+  out of sync with it.
+- **`relativeTime.*`** — `Today`, `Yesterday`, `{{ count }}d ago`, `{{ count }}w ago`, used by
+  `timestampFormatter(relativeCompact: true)`.
+
+Both are part of your catalog's types, so you override them exactly as before — `t('language.de')` is
+a checked key, and a typo in either is still a compile error.

examples/tutorial/package.json

@@ -16,7 +16,7 @@
     "emoji-mart": "^5.6.0",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
-    "stream-chat": "10.0.0-rc.4",
+    "stream-chat": "10.0.0-rc.5",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {

examples/vite/docs-playwright/take-tier1-screenshots.mjs

@@ -159,7 +159,9 @@ async function run() {
 
   console.log('\n✅ Done!');
   console.log('\n⚠ Not automated (need app-level config):');
-  console.log('  - Localization2.png — needs defaultLanguage="it" on Chat component');
+  console.log(
+    '  - Localization2.png — needs an it dictionary registered and language: "it" on the Streami18n instance',
+  );
   console.log('  - Diacritics.png — needs user with diacritical name in the channel');
   console.log(
     '  - Transliteration.png — needs useMentionsTransliteration prop + Cyrillic user',

examples/vite/package.json

@@ -17,7 +17,7 @@
     "modern-normalize": "^3.0.1",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
-    "stream-chat": "10.0.0-rc.4",
+    "stream-chat": "10.0.0-rc.5",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {

examples/vite/src/i18n/de.ts

@@ -594,11 +594,13 @@ export const deTranslations = {
   'notification.commandDisabled': 'Befehl nicht verfügbar',
   'notification.commandDisabledWhileEditing': 'Befehl beim Bearbeiten nicht verfügbar',
   'notification.commandDisabledWhileReplying': 'Befehl beim Antworten nicht verfügbar',
+  'notification.commandNotReady': 'Befehl kann noch nicht gesendet werden',
   'notification.dismissNotification.ariaLabel': 'Benachrichtigung schließen',
-  'notification.jumpToFirstUnreadFailed':
-    'Sprung zur ersten ungelesenen Nachricht fehlgeschlagen',
   'notification.list.notifications.ariaLabel': 'Benachrichtigungen',
   'notification.locationGetFailed': 'Standort konnte nicht ermittelt werden',
+  'notification.messageJumpFailed': 'Sprung zur Nachricht fehlgeschlagen',
+  'notification.messageJumpToLatestFailed':
+    'Sprung zur neuesten Nachricht fehlgeschlagen',
   'notification.locationShareFailed': 'Standort konnte nicht geteilt werden',
   'notification.pollCreateFailed': 'Umfrage konnte nicht erstellt werden',
   'notification.pollCreateFailedWithReason':
@@ -659,7 +661,6 @@ export const deTranslations = {
     'Mehr als eine Option auswählen',
   'poll.multipleAnswersField.typeNumber210.label': 'Gib eine Zahl von 2 bis 10 ein',
   'poll.nameField.askQuestion.placeholder': 'Stelle eine Frage',
-  'poll.nameField.error.text': 'Fehler',
   'poll.nameField.questionRequired.label': 'Eine Frage ist erforderlich',
   'poll.optionFieldSet.addOption.placeholder': 'Option hinzufügen',
   'poll.optionFieldSet.option.ariaLabel': 'Option {{ position }}',

examples/vite/src/i18n/it.ts

@@ -592,12 +592,14 @@ export const itTranslations = {
     'Comando non disponibile durante la modifica',
   'notification.commandDisabledWhileReplying':
     'Comando non disponibile durante la risposta',
+  'notification.commandNotReady': "Comando non pronto per l'invio",
   'notification.dismissNotification.ariaLabel': 'Chiudi la notifica',
-  'notification.jumpToFirstUnreadFailed':
-    'Impossibile passare al primo messaggio non letto',
   'notification.list.notifications.ariaLabel': 'Notifiche',
   'notification.locationGetFailed': 'Impossibile recuperare la posizione',
   'notification.locationShareFailed': 'Impossibile condividere la posizione',
+  'notification.messageJumpFailed': 'Impossibile passare al messaggio',
+  'notification.messageJumpToLatestFailed':
+    'Impossibile passare al messaggio più recente',
   'notification.pollCreateFailed': 'Impossibile creare il sondaggio',
   'notification.pollCreateFailedWithReason':
     'Impossibile creare il sondaggio a causa di {{reason}}',
@@ -655,7 +657,6 @@ export const itTranslations = {
     'Seleziona più di una opzione',
   'poll.multipleAnswersField.typeNumber210.label': 'Inserisci un numero da 2 a 10',
   'poll.nameField.askQuestion.placeholder': 'Fai una domanda',
-  'poll.nameField.error.text': 'Errore',
   'poll.nameField.questionRequired.label': 'La domanda è obbligatoria',
   'poll.optionFieldSet.addOption.placeholder': 'Aggiungi un’opzione',
   'poll.optionFieldSet.option.ariaLabel': 'Opzione {{ position }}',