背景

官方目前未打算支持 i18n 国际化路由支持，且尚未提供解决方案，但是我们可以通过实验特性 appDir 来实现。

Not Planned Features

We are currently not planning to include the following features in app:

• Internationalization (i18n) - we will be providing a guide on how to implement internationalization in app.
• AMP Support

If you need any of these features, we will continue to support pages, including bug fixes and feature additions, for multiple major versions.

文档地址： beta.nextjs.org/docs/app-di…

首先需要了解一下 Server and Client Components 服务器组件和客户端组件。

What do you need to do?	Server Component	Client Component
Fetch data. Learn more.	✅	⚠️
Access backend resources (directly)	✅	❌
Keep sensitive information on the server (access tokens, API keys, etc)	✅	❌
Keep large dependencies on the server / Reduce client-side JavaScript	✅	❌
Add interactivity and event listeners (onClick(), onChange(), etc)	❌	✅
Use State and Lifecycle Effects (useState(), useReducer(), useEffect(), etc)	❌	✅
Use browser-only APIs	❌	✅
Use custom hooks that depend on state, effects, or browser-only APIs	❌	✅
Use React Class components	❌	✅

简单来说，服务器端组件不支持事件侦听、不支持生命周期状态，这导致了原有的好多组件不可以直接拿来就用了。比如 next-i18next， next-themes 等等好多，直接引入使用会报各种莫名其妙的错误。

废话不多说，直接进入正题。

实现

i18n 方法

首先你需要一个 i18n 的实现，可以用 i18next，也可以用 rosetta 之类的。我这里实现了一个简化版的。

// 参考示例项目的 /i18n/next-i18n.ts
import dlv from 'dlv';
import tmpl from 'templite';

// eslint-disable-next-line no-unused-vars
type Fn = (...args: any[]) => string;
export interface I18nDict {
  [key: string]: string | number | Fn | I18nDict;
}

export interface NextI18nOptions {
  /**
   * Define the list of supported languages, this is used to determine if one of
   * the languages requested by the user is supported by the application.
   * This should be be same as the supportedLngs in the i18next options.
   */
  supportedLanguages: string[];
  /**
   * Define the fallback language that it's going to be used in the case user
   * expected language is not supported.
   * This should be be same as the fallbackLng in the i18next options.
   */
  fallbackLng: string;
}

export class NextI18n {
  private currentLocale: string;

  public fallbackLng: string;

  public supportedLanguages: string[];

  private dict: I18nDict = {};

  constructor(options: NextI18nOptions) {
    this.currentLocale = options.fallbackLng;
    this.supportedLanguages = options.supportedLanguages;
    this.fallbackLng = options.fallbackLng;
  }

  public locale = (lang?: string) => {
    if (lang !== undefined && this.currentLocale !== lang) {
      this.currentLocale = lang;
      this.onChangeLanguage?.(lang);
    }
    return this.currentLocale;
  };

  public set = (lang: string, dict: I18nDict) => {
    this.dict[lang] = Object.assign(this.dict[lang] || {}, dict);
  };

  public t = (key: string, params?: any, lang?: string): string => {
    // eslint-disable-next-line
    const val = dlv(this.dict[lang || this.currentLocale] as any, key, key);
    // eslint-disable-next-line
    if (typeof val === 'function') return val(params) as string;
    // eslint-disable-next-line
    if (typeof val === 'string') return tmpl(val, params);
    return val as string;
  };

  /* PROTECTED */
  // eslint-disable-next-line no-unused-vars
  private onChangeLanguage?: (locale: string) => void;

  // eslint-disable-next-line no-unused-vars
  public setOnChange = (fn: (locale: string) => void) => {
    this.onChangeLanguage = fn;
  };
}

然后是初始化这个 i18n 实例：

// 参考示例项目的 /i18n/index.ts
import { NextI18n } from './next-i18n';

export const languages = {
  'zh-CN': { name: '简体中文', flag: '🇨🇳', unicode: '1f1e8-1f1f3' },
  'zh-TW': { name: '正體中文', flag: '🇹🇼', unicode: '1f1f9-1f1fc' },
  en: { name: 'English', flag: '🇺🇸', unicode: '1f1fa-1f1f8' },
  ko: { name: '한국어', flag: '🇰🇷', unicode: '1f1f0-1f1f7' },
  ja: { name: '日本語', flag: '🇯🇵', unicode: '1f1ef-1f1f5' }
};

export const supportedLanguages = Object.keys(languages);
export const fallbackLng = 'zh-CN';

const i18n = new NextI18n({
  supportedLanguages,
  fallbackLng
});

supportedLanguages.forEach((locale) => {
  // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
  i18n.set(locale, require(`./${locale}/common.json`));
});

export default i18n;

Provider

注意 Provider 中用到了 useState 来强制刷新，所以必须是个 Client Component。

// 参考示例项目的 /i18n/provider.ts
'use client';

import {
  createContext,
  createElement,
  ReactNode,
  useMemo,
  useState
} from 'react';
import { NextI18n } from './next-i18n';

export const context = createContext<{ i18n: NextI18n } | null>(null);

interface I18nProviderProps {
  children: ReactNode;
  i18n: NextI18n;
}

export function I18nProvider({ i18n, children }: I18nProviderProps) {
  const [, setTick] = useState(0);

  const value = useMemo(() => {
    // eslint-disable-next-line
    i18n.setOnChange(() => {
      setTick((s) => s + 1);
    });
    return { i18n };
  }, [i18n]);

  // eslint-disable-next-line react/no-children-prop
  return createElement(context.Provider, {
    value: { ...value },
    children
  });
}

Hook

不用说，也是个 Client Component。

// 参考示例项目的 /i18n/hook.ts
'use client';

import { useContext } from 'react';
import { context } from './provider';

export function useI18n() {
  const content = useContext(context);
  if (!content) {
    throw new Error('Unable to get instance of i18n');
  }
  return content.i18n;
}

app 中创建

不要直接在 layout、page 中使用 Client Component，所以我又在 Provider 上套了一层。

// laoyout.tsx
// 手动套一层 provider
import { I18nClientProvider } from './providers';

export default function RootLayout({
  children,
  params
}: {
  children: React.ReactNode;
  params: { locale: string };
}) {
  const { locale = 'zh-CN' } = params || {};

  return (
    <I18nClientProvider locale={locale}>
      <html lang={locale}>
        <head />
        <body>
          <div className='pt-20' style={{ minHeight: 'calc(100vh - 75px)' }}>
            {children}
          </div>
        </body>
      </html>
    </I18nClientProvider>
  );
}

这个 Provider 的代码为：

'use client';
import { I18nProvider, i18n } from '@/i18n';
import { useEffect } from 'react';

export function I18nClientProvider({
  children,
  locale
}: {
  children: React.ReactNode;
  locale: string;
}) {
  useEffect(() => {
    if (i18n.locale() !== locale) {
      i18n.locale(locale);
    }
  }, [locale]);

  return <I18nProvider i18n={i18n}>{children}</I18nProvider>;
}

最后

• 附上示例项目代码： github.com/willin/beta…
• 示例项目演示地址： willin-wang-ndd35eg64-willin.vercel.app/