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Next.js

Dynamically Set HTML Lang Attribute in Next.js

By Filip on 10/05/2024

Learn how to dynamically set the HTML lang attribute in your Next.js application for improved accessibility and SEO.

Dynamically Set HTML Lang Attribute in Next.js

Table of Contents

Introduction

In this article, we'll explore how to dynamically set the lang attribute of the <html> tag in your Next.js application based on the user's language. This is crucial for improving accessibility and SEO by providing the browser with information about the language of your content. We'll cover determining the user's language, creating a custom _document.js file, accessing and passing the language to this file, and finally, rendering the lang attribute. Let's dive in and make your Next.js application more language-aware.

Step-by-Step Guide

To dynamically set the lang attribute of the <html> tag in your Next.js application based on the user's language, you can follow these steps:

1. Determine the User's Language:

  • You can use a library like next-i18next or implement your own logic to determine the user's preferred language. This could involve checking browser settings, user preferences stored in cookies, or routing parameters.

2. Create a Custom _document.js File:

  • Next.js allows you to customize the <html> and <body> tags by creating a _document.js file inside your pages directory.
// pages/_document.js
import Document, { Html, Head, Main, NextScript } from 'next/document';

class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const initialProps = await Document.getInitialProps(ctx);
    // Determine the language here (e.g., from cookies or context)
    const lang = ctx.req ? ctx.req.headers['accept-language'] : 'en';
    return { ...initialProps, lang };
  }

  render() {
    return (
      <Html lang={this.props.lang}>
        <Head />
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

export default MyDocument;

3. Access and Pass the Language to _document.js:

  • In the getInitialProps method of your custom _document.js, you can access the request object (ctx.req) to get the user's preferred language from headers, cookies, or any other relevant source.
  • Pass the determined language as a prop to the Html component.

4. Render the lang Attribute:

  • In the render method of your custom _document.js, access the language prop and set it as the value of the lang attribute for the <html> tag.

Explanation:

  • The _document.js file allows you to customize the initial HTML structure of your Next.js application.
  • By overriding the getInitialProps method, you can fetch data during the server-side rendering process, including the user's language preference.
  • The Html component from next/document represents the <html> tag, and you can pass props to it, including the dynamically determined lang attribute.

Note:

  • This approach ensures that the lang attribute is set on the server-side, which is important for SEO and accessibility.
  • Remember to replace the placeholder logic for determining the language with your own implementation based on your application's requirements.

Code Example

This code defines a custom Next.js document (_document.js) to dynamically set the HTML language attribute based on user preferences. It extracts language information from cookies or headers, providing a basic example of internationalization setup.

// pages/_document.js
import Document, { Html, Head, Main, NextScript } from 'next/document';
import { useRouter } from 'next/router';

class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const initialProps = await Document.getInitialProps(ctx);
    // Determine the language from cookies, headers, or any other method
    const lang = getLanguageFromRequest(ctx.req); 
    return { ...initialProps, lang };
  }

  render() {
    return (
      <Html lang={this.props.lang}>
        <Head />
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

// Helper function to determine language from request
function getLanguageFromRequest(req) {
  // Example: Get language from cookies
  if (req.cookies.language) {
    return req.cookies.language;
  }

  // Example: Get language from 'Accept-Language' header
  if (req.headers['accept-language']) {
    const acceptedLanguages = req.headers['accept-language'].split(',');
    return acceptedLanguages[0].split(';')[0].trim(); 
  }

  // Default language
  return 'en';
}

export default MyDocument;

Explanation:

  1. Import Necessary Modules:

    • Import Document, Html, Head, Main, and NextScript from next/document to customize the document structure.
    • Import useRouter from next/router if you need to access routing information.

  2. Create a Custom _document.js:

    • Define a class MyDocument that extends the Document class from next/document.

  3. Get Initial Props:

    • Use the getInitialProps static method to fetch data during server-side rendering.
    • Call Document.getInitialProps(ctx) to get the default props.
    • Implement the getLanguageFromRequest function to determine the user's language based on your logic (e.g., cookies, headers).
    • Return the default props along with the determined language.

  4. Render the Document:

    • In the render method, access the lang prop passed from getInitialProps.
    • Set the lang attribute of the <Html> component to the dynamically determined language.

  5. Helper Function getLanguageFromRequest:

    • This function demonstrates how to extract the language from different sources:
      • Cookies: Check if a language cookie exists.
      • Headers: Parse the Accept-Language header to get the user's preferred languages.
    • You can customize this function to implement your own language detection logic.

How to Use:

  1. Create the pages/_document.js file in your Next.js project.
  2. Paste the code into the file.
  3. Customize the getLanguageFromRequest function to match your language detection implementation.

Now, when a user visits your Next.js application, the <html> tag will dynamically have the lang attribute set based on their preferred language.

Additional Notes

Importance of lang Attribute:

  • Accessibility: Screen readers and other assistive technologies rely on the lang attribute to determine the correct pronunciation and language-specific features.
  • SEO: Search engines use the lang attribute to understand the language of your content, which helps with ranking in relevant search results.
  • User Experience: Setting the correct language helps browsers display fonts, hyphenation, and other typographic features correctly.

Best Practices for Language Detection:

  • Prioritize User Preferences: Allow users to explicitly set their preferred language through language switchers or account settings. Store this preference in cookies or local storage.
  • Use Accept-Language Header with Caution: The Accept-Language header provides a list of user's preferred languages, but it's not always accurate and should be used as a fallback option.
  • Handle Language Fallbacks: Define a default language for your application in case the user's preferred language is not available or cannot be determined.

Additional Considerations:

  • Right-to-Left (RTL) Languages: If your application supports RTL languages, you'll also need to dynamically set the dir attribute on the <html> tag to "rtl" for those languages.
  • Language Negotiation: For more complex scenarios, consider implementing language negotiation strategies based on URL parameters, domain names, or user geolocation.
  • Caching: Be mindful of caching when dynamically setting the lang attribute. Ensure that the correct language is served to each user, especially if using server-side rendering or static site generation.

Testing:

  • Test with Different Browsers and Assistive Technologies: Ensure that the lang attribute is correctly set and interpreted by different browsers and assistive technologies.
  • Use Language-Specific Validation Tools: Validate your HTML markup using language-specific validators to catch any errors related to language declaration or character encoding.

Summary

This table summarizes how to dynamically set the <html> tag's lang attribute based on user language in a Next.js application:

Step Description Code Example
1. Determine User Language - Use libraries like next-i18next or custom logic.
- Check browser settings, cookies, or routing parameters.		 const lang = ctx.req ? ctx.req.headers['accept-language'] : 'en';
2. Create Custom _document.js - Create _document.js inside the pages directory.
- Customize <html> and <body> tags.		 javascript import Document, { Html, Head, Main, NextScript } from 'next/document'; // ... rest of the code
3. Access and Pass Language - In _document.js's getInitialProps, access the request object (ctx.req).
- Get the user's preferred language.
- Pass the language as a prop to the Html component.		 javascript static async getInitialProps(ctx) { // ... return { ...initialProps, lang }; } // ... <Html lang={this.props.lang}>
4. Render lang Attribute - In _document.js's render method, access the language prop.
- Set it as the value of the lang attribute for the <html> tag.		 javascript render() { return ( <Html lang={this.props.lang}> // ... </Html> ); }

Key Points:

  • _document.js customizes the initial HTML structure.
  • Overriding getInitialProps fetches data during server-side rendering.
  • The Html component represents the <html> tag and accepts props.
  • Setting the lang attribute server-side is crucial for SEO and accessibility.
  • Replace placeholder language determination logic with your application's requirements.

Conclusion

By following these steps, you can effectively set the lang attribute dynamically in your Next.js application, enhancing its accessibility and SEO. This approach ensures that the language is set server-side, providing the correct language information to search engines and assistive technologies from the initial page load. Remember to tailor the language detection logic to your specific needs and consider best practices for handling user preferences and fallbacks. By dynamically managing the lang attribute, you create a more inclusive and user-friendly experience for a global audience.

References

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