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hi18n: message internationalization meets immutability and type-safety

Quickstart

Installation:

npm install @hi18n/core @hi18n/react-context @hi18n/react
npm install -D @hi18n/cli

# Or:

yarn add @hi18n/core @hi18n/react-context @hi18n/react
yarn add -D @hi18n/cli

Put the following file named like src/locale/index.ts:

import { Book, Catalog, Message, msg } from "@hi18n/core";

type Vocabulary = {
  "example/greeting": Message<{ name: string }>;
};
const catalogEn = new Catalog<Vocabulary>("en", {
  "example/greeting": msg("Hello, {name}!"),
});
export const book = new Book<Vocabulary>({ en: catalogEn });

And you can use the translation anywhere like:

import React from "react";
import { useI18n } from "@hi18n/react";
import { book } from "../locale";

export const Greeting: React.FC = () => {
  // Locale can be configured via <LocaleProvider>
  const { t } = useI18n(book);
  return <p>{t("example/greeting", { name: "John" })}</p>;
};

Instead of useI18n, you can also use the following items for translation:

  • getTranslator from @hi18n/core
  • <Translate> component from @hi18n/react

Updating vocabularies and catalogs

To update vocabularies and catalogs, first put a configuration:

module.exports = {
  // The files that hi18n should read
  include: ["src/**/*.ts", "src/**/*.tsx"],
};

Then use the following command to synchronize vocabularies and catalogs:

hi18n sync

Alternatively you can directly specify what files to include:

hi18n sync 'src/**/*.ts' 'src/**/*.tsx'

It does the following:

  • It collects all book definitions, catalog definitions, vocabulary definitions and translation usages in the given files.
  • For each books:
    • If there are unused translation in the vocabulary or in the catalogs, it comments out the relavant definitions.
    • If there are missing translation referenced from somewhere, it adds the skeleton convenient for working on the translation. If there are previously commented out definitions, it instead uncomments these lines.

Adding new translations

Implementation-first way

You can use "todo" versions of the translation functions:

  • t.todo("example/new") instead of t("example/new")
  • <Translate.Todo id="example/new" book={book} /> instead of <Translate id="example/new" book={book} />

Then run hi18n sync and the CLI automatically prepares the skeleton for you.

(Ideally hi18n sync should also remove the .todo part but it is not implemented yet)

Translation-first way

You can manually edit your data, and then add the corresponding implementation that makes use of the new translation.

Dynamically selecting translation ids

You can use translationId in conjunction with t.dynamic to select translation ids dynamically.

const menus = [
  {
    url: "https://example.com/home",
    titleId: translationId("menu/home/title"),
    tooltipId: translationId("menu/home/tooltip"),
  },
  {
    url: "https://example.com/map",
    titleId: translationId("menu/map/title"),
    tooltipId: translationId("menu/map/tooltip"),
  },
];

// Translate menu title
t.dynamic(menus[i].titleId); // Works like t("menu/home/title")

There is also <Translate.Dynamic/> which works like <Translate/>.

Concepts

  • Translation id
    • A string representing a message to be translated. It can be arbitrary strings but we recommend using one of:
      • Slash-separated names like example/greeting
      • Or, message in your project's main language like Hello, {name}!
  • Translated message
    • A message in each locale, like こんにちは、{name}さん!. It may contain placeholders.
  • Catalog
    • A set of translated messages in a specific locale. More precisely, it contains a mapping from translation ids to translation messages.
  • Book
    • A set of catalogs over all supported locales.
    • A project may contain multiple books. This is useful for splitting data to reduce chunk sizes.
  • Locale provider
    • Something that tells you the current locale.
    • Existing locale providers:
      • @hi18n/react
      • Custom locale provider
  • Translator, translation helper
    • The actual function to get the translated and evaluated message.
    • You can acquire a translator by supplying a book and the current locale.

Books and locale providers are orthogonal. You can have multiple books and multiple locale providers in a single project.

You combine books and locales in each file. It may require you some effort at first, but provides the better experience in the long run.

// useI18n -- locale provider
import { useI18n } from "@hi18n/react";
// book
import { book } from "../locale";

// You do this in each file
const { t } = useI18n(book);

File layout

Referencing catalogs from books

Catalogs must be referenced by one of the following ways:

  • Single-file configuration: referenced as a toplevel file-scope local variable in the same file
  • Multi-file configuration: referenced as a module export

In the single-file configuration, it is recommended to use the name catalogEn for English for example.

// Top-level file-scope local variables
const catalogEn = new Catalog<Vocabulary>("en", { ... });
const catalogJa = new Catalog<Vocabulary>("ja", { ... });
export const book = new Book<Vocabulary>({
  en: catalogEn,
  ja: catalogJa,
});

In the multi-file configuration, it is recommended to use the default exports.

// en.ts
export default new Catalog<Vocabulary>("en", { ... });

// ja.ts
export default new Catalog<Vocabulary>("ja", { ... });

// index.ts
import catalogEn from "./en";
import catalogJa from "./ja";
export const book = new Book<Vocabulary>({
  en: catalogEn,
  ja: catalogJa,
});

Referencing books from the application code

Books must also be referenced by one of the following ways:

  • Single-file configuration: referenced as a toplevel file-scope local variable in the same file
  • Multi-file configuration: referenced as a module export

Multi-file configuration is recommended. In that case, it is recommended to use the name book for the export.

// src/locale/index.ts
export const book = new Book<Vocabulary>({ ...  });

// src/components/greeting.ts
import { book } from "../locale";
const { t } = useI18n(book);

Message syntax

Message roughly resembles ICU MessageFormat.

  • Simple message: Hello, world!
  • Interpolation: Hello, {name}!
  • Interleaving with markups: Please <link>read the license agreement</link> before continuing.

See formatting.md for more details.

Loading only a specific language

If you have many languages to support, you want to load only a specific locale. This is possible by the following steps:

  1. Declare dynamic loading in a book
  2. Preload catalogs before rendering

Declare dynamic loading in a book

Switch from:

import catalogEn from "./en";
import catalogJa from "./ja";

export const book = new Book<Vocabulary>({
  en: catalogEn,
  ja: catalogJa,
});

to:

export const book = new Book<Vocabulary>({
  en: () => import("./en"),
  ja: () => import("./ja"),
});

Then hi18n does not load the catalogs immediately; instead you need to tell hi18n to load a specific catalog when you know which language to use.

Preload catalogs before rendering

Switch from:

// Start the app
root.render(
  <LocaleProvider locales="en">
    <App />
  </LocaleProvider>
);

to:

import { book } from "./path/to/translations";
import { preloadCatalogs } from "@hi18n/core";

await preloadCatalogs(book, "en");

// Start the app
root.render(
  <LocaleProvider locales="en">
    <App />
  </LocaleProvider>
);

to ensure catalogs are loaded before rendering.

You may want to use Promise.prototype.then instead:

import { book } from "./path/to/translations";
import { preloadCatalogs } from "@hi18n/core";

preloadCatalogs(book, "en")
  .then(() => {
    // Start the app
    root.render(
      <LocaleProvider locales="en">
        <App />
      </LocaleProvider>
    );
  })
  .catch((e) => {
    console.error("load error");
  });

Alternative: React Suspense

If you are using React, you may instead use React Suspense to wait for the translations to be loaded.

// Start the app
root.render(
  <LocaleProvider locales="en">
    {/* when the translations are not yet available, loadingPage will be shown */}
    <React.Suspense fallback={loadingPage}>
      <App />
    </React.Suspense>
  </LocaleProvider>
);

Then simply use the React API (useI18n or <Translate>) against dynamically loaded books.

This is an experimental API which relies on React's undocumented API for suspension. The feature may break if React removes or changes the undocumented API.