@comvi/svelte wraps @comvi/core for Svelte. setI18nContext() registers the instance for descendants; useI18n() returns reactive stores that work with $store syntax in both Svelte 4 and Svelte 5.

Same t() and <T> API as the Vue, React, and SolidJS bindings — switch frameworks without relearning your i18n layer.

📖 Documentation: https://comvi.io/docs/i18n/svelte/

Why Comvi i18n?

Comvi i18n is a modern, framework-agnostic internationalization library built on three principles: type-safe translations, real ICU MessageFormat, and zero compromises on bundle size or security.

• Rich text without XSS. Embed components inside translation strings (Click <link>here</link>) — translators see clean markup, you decide what each tag renders to. No raw HTML, no unsafe DOM injection, no splitting a sentence across template fragments.
• Real ICU MessageFormat. Plurals, ordinals, and select all follow locale-correct grammar via Intl.PluralRules — Polish, Ukrainian, Arabic, Welsh, and the rest. Same syntax every major TMS (Crowdin, Lokalise, Phrase) already speaks.
• Locale-aware formatters built in. formatNumber, formatDate, formatCurrency, and formatRelativeTime follow the active locale via native Intl, with reactive updates in every framework binding.
• ~8 kB gzipped, zero runtime dependencies. No eval or new Function anywhere — runs under a strict CSP without unsafe-eval. Safe for Chrome extensions, Cloudflare Workers, and locked-down enterprise apps.
• Pluggable, not monolithic. Translation loading (CDN/API), locale detection, and in-context editing are opt-in plugins via @comvi/plugin-fetch-loader, @comvi/plugin-locale-detector, and @comvi/plugin-in-context-editor. You only ship what you use.
• Same API across 6 frameworks. useI18n() and <T> look the same in Vue, React, SolidJS, Svelte, Next.js, and Nuxt — switch frameworks without relearning your i18n layer.

Why @comvi/svelte?

• Native stores with $ syntax. useI18n() returns proper Svelte stores — $locale, $isLoading, $t() work seamlessly with auto-subscription in templates.
• Single context setup. Call setI18nContext() once in a parent component; descendants automatically access stores via useI18n() without prop drilling.
• Both Svelte 4 & 5. Built with Svelte 5's rune-compatible API while remaining fully compatible with Svelte 4 projects.

Install

npm install @comvi/svelte
# Peer: svelte ^4.0.0 || ^5.0.0

Quick start

<!-- src/routes/+layout.svelte (or App.svelte) -->
<script lang="ts">
  import { createI18n, setI18nContext } from "@comvi/svelte";

  const i18n = createI18n({
    locale: "en",
    fallbackLocale: "en",
    translation: {
      en: { greeting: "Hello, {name}!" },
      uk: { greeting: "Привіт, {name}!" },
    },
  });

  setI18nContext(i18n);
</script>

<slot />

<!-- A child component -->
<script lang="ts">
  import { useI18n } from "@comvi/svelte";
  const { t, locale, setLocale } = useI18n();
</script>

<h1>{$t("greeting", { name: "Alice" })}</h1>
<select value={$locale} on:change={(e) => setLocale(e.currentTarget.value)}>
  <option value="en">English</option>
  <option value="uk">Українська</option>
</select>

For strict typed key overloads in Svelte, use tRaw from useI18n(). The $t store is a string-key convenience wrapper for template ergonomics.

For <T> rich-text components, type-safe keys, and the full store API, see the documentation.

Rich text with <T>

Tag interpolation lets translators write readable markup like "Click <link>here</link> for help" without raw HTML or XSS risk. Map tags to standard HTML elements or custom attributes:

{
  "help": "For support, <link>visit our docs</link> or <bold>email us</bold>.",
  "legal": "See our <policy>privacy policy</policy>."
}

<script lang="ts">
  import { T } from "@comvi/svelte";
</script>

<T
  i18nKey="help"
  components={{
    link: "a",    // Map to standard HTML tag
    bold: "strong",
    policy: { tag: "a", props: { href: "/privacy" } },
  }}
/>

<!-- Renders: "For support, <a>visit our docs</a> or <strong>email us</strong>." -->
<!-- policy becomes: <a href="/privacy">See our privacy policy</a> -->

The <T> component escapes text and filters rendered tags/attributes before using Svelte's HTML rendering path. Props can inject attributes; translators see only the text.

ICU MessageFormat — locale-correct grammar, not just singular/plural

count === 1 ? "item" : "items" works in English. It silently ships broken grammar in Polish, Ukrainian, Arabic, Welsh, and 30+ other locales — those languages have 3, 4, sometimes 6 distinct plural categories that a binary if/else can't express. ICU MessageFormat is the standard syntax for handling them — the same syntax Crowdin, Lokalise, Phrase, and every major TMS already speak. Comvi i18n parses it via native Intl.PluralRules, so every CLDR plural category is correct by default.

Plurals across languages

{
  "en": { "messages": "{count, plural, one {# message} other {# messages}}" },
  "uk": {
    "messages": "{count, plural, one {# повідомлення} few {# повідомлення} many {# повідомлень} other {# повідомлення}}"
  },
  "ar": {
    "messages": "{count, plural, zero {لا توجد رسائل} one {رسالة واحدة} two {رسالتان} few {# رسائل} many {# رسالة} other {# رسالة}}"
  }
}

t("messages", { count: 0 }); // ar: "لا توجد رسائل"      (zero form)
t("messages", { count: 1 }); // en: "1 message"            uk: "1 повідомлення"
t("messages", { count: 5 }); // en: "5 messages"           uk: "5 повідомлень"          ar: "5 رسائل"
t("messages", { count: 22 }); // uk: "22 повідомлення"  ← the "few" form, NOT the "many" form

A naive English-style count === 1 ? singular : plural picks one Ukrainian form and ships it for every count — grammatically wrong for half your traffic.

Ordinals (1st, 2nd, 3rd…)

{ "rank": "{place, selectordinal, one {#st} two {#nd} few {#rd} other {#th}}" }

t("rank", { place: 1 }); // "1st"
t("rank", { place: 22 }); // "22nd"
t("rank", { place: 113 }); // "113th"

Select (gender, role, status)

{ "greeting": "{gender, select, female {Welcome, madam} male {Welcome, sir} other {Welcome}}" }

t("greeting", { gender: "female" }); // "Welcome, madam"
t("greeting", { gender: "male" }); // "Welcome, sir"
t("greeting", { gender: "other" }); // "Welcome"

Locale-aware Intl formatters

Numbers, dates, currency, and relative time follow the active locale via native Intl — reactive in your framework binding:

<script lang="ts">
  import { useI18n } from "@comvi/svelte";

  const { t, locale, setLocale, formatNumber, formatDate, formatCurrency, formatRelativeTime } = useI18n();
  let itemCount = 5;
</script>

<!-- Plurals automatically match locale -->
<p>{$t("items", { count: itemCount })}</p>

<!-- Locale-aware formatting — automatically updates when locale changes -->
<p>Users: {formatNumber(1234.5)}</p>
<p>Total: {formatCurrency(99.99, "USD")}</p>
<p>Updated: {formatDate(new Date())}</p>
<p>Posted: {formatRelativeTime(-2, "hour")}</p>

<select value={$locale} on:change={(e) => setLocale(e.currentTarget.value)}>
  <option value="en">English</option>
  <option value="uk">Українська</option>
</select>

With translation: "items": "{count, plural, one {# item} other {# items}}" and itemCount = 5, renders: "5 items".

Type-safe translation keys

Declare translation keys once to type the core API and framework bindings. In Svelte, tRaw keeps the typed overloads from core; $t is the string convenience store and accepts string keys.

// src/types/i18n.d.ts
declare module "@comvi/core" {
  interface TranslationKeys {
    welcome: { name: string }; // name param required
    greeting: never; // no params
    items: { count: number };
    "errors:NOT_FOUND": never;
  }
}

<script lang="ts">
  import { useI18n } from "@comvi/svelte";
  const { tRaw } = useI18n();

  // ✓ Compiles — params shape matches the declaration
  const welcome = $tRaw("welcome", { name: "Alice" });
</script>

<h1>{welcome}</h1>

What TypeScript catches:

// ✗ Expected 2 arguments, but got 1
$tRaw("welcome");

// ✗ Property 'name' is missing in type '{ age: number }'
$tRaw("welcome", { age: 5 });

// ✗ Type 'number' is not assignable to type 'string'
$tRaw("welcome", { name: 42 });

// ✗ Argument of type '"typo"' is not assignable to parameter
$tRaw("typo", { name: "Alice" });

Auto-generate these types from the Comvi platform via @comvi/cli or from local JSON with @comvi/vite-plugin.

Loading translations from the Comvi platform

Pair with @comvi/plugin-fetch-loader to load translations from a CDN or API. No redeploy needed to ship a translation:

<!-- src/routes/+layout.svelte -->
<script lang="ts">
  import { createI18n, setI18nContext } from "@comvi/svelte";
  import { FetchLoader } from "@comvi/plugin-fetch-loader";

  const i18n = createI18n({ locale: "en" });

  // CDN for production, API for dev/staging
  i18n.use(FetchLoader({
    cdnUrl: "https://cdn.comvi.io/your-distribution-id",
  }));

  setI18nContext(i18n);
</script>

<slot />

See @comvi/plugin-fetch-loader for full options and API endpoints.

License

MIT © Comvi