By Buka Corner in Standards — Oct 24, 2024

Understanding ISO Language Codes and the IETF BCP 47 Standard: A Simple Guide for Beginners

If you've ever switched languages on a website or app, you've likely seen short codes like "en" for English or "fr" for French. These are called ISO language codes, and they play a vital role in ensuring that every language is identified uniquely. But there's another standard at play when you see combinations like "en-US" — that's the IETF BCP 47 standard. This guide will help you understand both ISO language codes and IETF language tags, and why they matter.

What Are ISO Language Codes?

ISO language codes are part of the ISO 639 standard, which provides a set of codes to represent languages. This standard is divided into different parts to cater to different needs:

ISO 639-1: The most commonly used, it consists of two-letter codes like "en" for English and "id" for Indonesian. These codes are widely used in apps, websites, and software where the most common languages need to be represented in a compact format.
ISO 639-2: This expands the code list to three-letter codes, such as "eng" for English or "ind" for Indonesian. It includes a wider variety of languages and is often used in libraries, databases, and by researchers dealing with more specific language information.
ISO 639-3: The most comprehensive of all, it covers every known language using three-letter codes, even those spoken by small communities. It’s particularly useful in linguistic research and academic settings.

These codes ensure that every language, from widely spoken ones to obscure dialects, is represented in a standardized and unique way.

The IETF BCP 47 Standard: Language Tags for Regional Variations

While ISO codes identify languages, the IETF BCP 47 standard goes a step further by allowing us to specify regional or dialectical variations of a language. These language tags combine the language code from ISO 639 with a region code from the ISO 3166-1 standard, which represents countries.

For example:

"en-US" stands for English as spoken in the United States.
"en-GB" represents English as spoken in the United Kingdom.
"id-ID" means Indonesian as spoken in Indonesia.

Here’s how it works:

Language code: The part before the hyphen, like "en" or "id," represents the base language. These come from ISO 639.
Region code: The part after the hyphen, like "US" for the United States or "ID" for Indonesia, comes from ISO 3166 and refers to the country or region.

Why Use Language Tags?

Using IETF BCP 47 language tags allows systems to be region-aware. While "en" refers to English in general, "en-US" and "en-GB" help specify whether the content should use American English or British English. This matters for differences in spelling, date formatting, and even terminology. For example:

"color" in American English vs. "colour" in British English.
The date "12/31/2024" (December 31st) in the US would be "31/12/2024" in the UK.

By combining language and region codes, IETF BCP 47 ensures that users get a localized experience that feels natural to them, based on where they are or the language they speak.

Are Language Codes and Tags Unique?

Yes, both ISO language codes and IETF language tags are designed to be unique within their context:

ISO 639 codes ensure that no two languages share the same code. For example, "en" will always refer to English.
IETF BCP 47 tags are also unique because they combine language codes and region codes in specific ways, like "en-US" or "fr-CA" (French in Canada).

This ensures that systems can identify languages and their regional variations precisely without any overlap.

Other Points You Should Know

In addition to the language and region, IETF BCP 47 tags can also include optional subtags for things like:

Script: To indicate a specific script used to write the language. For example, "zh-Hans" refers to Simplified Chinese.
Variant: To indicate different versions or dialects of a language. For example, "sl-rozaj" refers to the Resian dialect of Slovenian.

These subtags allow for even more granular control over language localization, ensuring that content is displayed correctly for users with very specific linguistic needs.

When Should You Use These Codes and Tags?

Developing Multilingual Applications: If you're building an app that supports multiple languages and regions, using both ISO codes and IETF tags ensures that users get the right content for their language and region.
Data Exchange: In databases or APIs where you need to pass language data between systems, these standardized codes help avoid confusion.
Localization: If you're localizing content for different regions, IETF tags help ensure that the right regional variations of the language are used.

Finally

Both ISO language codes and IETF BCP 47 language tags are essential tools for managing languages in a globalized world. While ISO codes give us a clear way to identify languages, IETF tags help us fine-tune the experience by taking regional and dialectal differences into account.

The next time you encounter codes like "en-US" or "fr-CA" you’ll know they’re not just random combinations. They represent a well-structured system to ensure that users get the right language and regional experience, making everything from browsing websites to using apps feel more natural and personalized.