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Understanding BCP 47 and ISO 639: The Key Differences and Considerations

Understanding BCP 47 and ISO 639: The Key Differences and Considerations
Photo by Yash Raut / Unsplash

When dealing with language identification in technology, there are two standards that are frequently mentioned: BCP 47 and ISO 639. While they might seem similar, they serve different purposes and are used in distinct contexts. In this article, we’ll explore the key differences between BCP 47 and ISO 639, and clarify how and when each is applied in real-world scenarios. Additionally, we’ll highlight some additional considerations that you may find useful when choosing which standard to use in your projects.

What is ISO 639?

ISO 639 is a set of standards designed to define language codes that are universally recognized. These codes help identify languages in a standardized manner across different platforms and systems. ISO 639 is broken down into several parts:

  1. ISO 639-1: This part of the standard provides two-letter (alpha-2) language codes. For example:
    • en for English
    • fr for French
    • de for German
  2. ISO 639-2: This part expands on ISO 639-1 with three-letter (alpha-3) codes. These are used for languages where the two-letter code may not be sufficient or when a more detailed code is needed:
    • eng for English
    • fra for French
    • deu for German
  3. ISO 639-3: This part is the most comprehensive, providing codes for all known languages across the globe, including dialects and regional languages that might not be covered by ISO 639-1 or ISO 639-2.

ISO 639 is focused entirely on languages, and it’s a crucial part of ensuring that language data is identified correctly across different systems.

What is BCP 47?

BCP 47, or Best Current Practice 47, is a broader standard developed by the Internet Engineering Task Force (IETF) to define language tags for use in various web and software applications. While it includes language codes from ISO 639, it goes a step further by also incorporating codes for scripts (ISO 15924), regions (ISO 3166), and even variants. This makes BCP 47 ideal for complex scenarios, like localization and internationalization of websites, apps, or services.

A BCP 47 tag can look like this:

  • en-US: English (language) as used in the United States (region)
  • fr-CA: French (language) as spoken in Canada (region)
  • zh-Hans-CN: Chinese (language) in Simplified script (script), spoken in China (region)

Key Components of a BCP 47 Tag:

  • Language Code: Derived from ISO 639 (e.g., en for English, fr for French).
  • Script Code: An optional code from ISO 15924 that specifies the script used for writing the language (e.g., Hans for Simplified Chinese).
  • Region Code: An optional code from ISO 3166-1 that specifies the country or geographical region (e.g., US for the United States).
  • Variants and Extensions: Additional components that can specify dialects, formatting preferences, or other linguistic distinctions.

Example BCP 47 Tags:

  • en-GB: English, as used in Great Britain
  • es-MX: Spanish, as spoken in Mexico
  • pt-BR: Portuguese, as spoken in Brazil
  • de-CH: German, as spoken in Switzerland

In essence, BCP 47 is a language tagging system that allows you to combine multiple elements (language, region, script, etc.) to create a detailed description of a language and its usage context.

BCP 47 vs ISO 639: Key Differences

Now that we understand the basics of both ISO 639 and BCP 47, let's highlight the key differences between them:

1. Scope and Purpose

  • ISO 639 is focused solely on identifying languages. It defines the language code, which can be two-letter (ISO 639-1), three-letter (ISO 639-2), or even three-letter dialectal codes (ISO 639-3).
  • BCP 47, on the other hand, is a language tag system. It allows you to combine language, region, script, and even variant codes into a single, unified identifier.

2. Granularity and Flexibility

  • ISO 639 provides a simplified approach with just language codes. It’s useful when you need to reference the language alone, without needing any additional contextual information.
  • BCP 47 is more flexible and detailed, offering the ability to specify not just the language, but also the geographical region, writing system, and even specific dialects or variants. This is important for projects that require localization and internationalization, where language usage might differ based on location or cultural context.

3. Use Cases

  • ISO 639 is often used when you need to simply identify a language, such as in databases, API responses, or language settings in systems.
  • BCP 47 is commonly used in web technologies, such as HTTP headers, HTML documents, and localization settings for websites or apps. It allows more precise identification of language preferences for users in different regions or speaking different dialects.

4. Inclusion of Other Components

  • While ISO 639 only deals with language codes, BCP 47 can include a script (from ISO 15924), region (from ISO 3166), and other elements like extensions and variants for a more complete description of a language’s context.

Other Considerations When Choosing Between BCP 47 and ISO 639

While the distinctions between BCP 47 and ISO 639 are clear, there are some important factors to keep in mind when deciding which to use in your projects:

  1. Localization Needs: If you’re working on a project that requires localization, such as a website or mobile app, BCP 47 will likely be the best choice. It allows you to specify not just the language, but also how the language is used regionally or culturally, making it highly useful for addressing user preferences.
  2. Internationalization: If you need to ensure that your system can handle multiple languages and cultural contexts seamlessly, BCP 47 provides the necessary structure to define and manage localized content more effectively.
  3. Database Design: If you're building a database that needs to track language preferences or support multi-language functionality, you might rely on ISO 639 codes for simplicity and integration, then expand to BCP 47 tags when more context (like region or script) is needed.
  4. Web Standards: For web-based applications, BCP 47 is used across several W3C specifications, including HTML and HTTP, and is commonly implemented in HTTP headers (Accept-Language) to determine the appropriate language for a webpage.
  5. Fallback Mechanisms: In some cases, you may use BCP 47 tags with fallback options, such as en-GB falling back to en (English) if the more specific tag is not available. This gives more flexibility in managing content for users from different regions.

Finally

Both BCP 47 and ISO 639 are essential in the world of language processing, and choosing between them depends on your specific use case. ISO 639 provides a foundation for identifying languages, while BCP 47 builds on this foundation, offering a richer and more detailed way to tag languages, regions, scripts, and variants.

For most modern web applications, BCP 47 is the recommended standard, as it allows greater precision and is already integrated into web standards. However, if you only need to identify a language without the added complexity of regions or scripts, ISO 639 may be sufficient.

When working with these standards, remember that context is key—understanding what your system needs will guide you in selecting the right approach.

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