ISO 21720:2024

Overview

ISO 21720:2024 specifies the XLIFF (XML Localization Interchange File Format) family for exchanging localizable content between tools and processes. Published as the second edition of ISO 21720, this document standardizes XLIFF 2.x behaviour to enable interoperability, lossless interchange of source and translated text, and modular extension for real-world localization workflows. The edition documents major updates (notably features introduced in XLIFF 2.1) such as advanced validation and native support for ITS 2.0 while also tightening schema-level constraints for language attributes.

Key Topics and Technical Requirements

• Core specification: minimal XML elements and attributes required to extract, carry and merge localized content. The core uses the namespace urn:oasis:names:tc:xliff:document:2.0.
• Conformance and processing rules: definitions for Agents (Extractor, Enricher, Writer, Merger), processing operations (Extraction, Enriching, Modification, Merging) and normative interpretation of requirement keywords (RFC 2119).
• Fragment identification & selectors: mechanisms to reference parts of documents for fine-grained processing and merging.
• Inline content and segmentation: rules for inline codes, annotations, sub-flows, bidirectional text and segment representation/order.
• Modules and extensions: optional modules with separate namespaces and schemas, including Translation Candidates, Glossary, Format Style, Metadata, Resource Data, Size & Length, Validation and the ITS Module (integration with ITS 2.0). Change Tracking is defined as an extension.
• Validation artifacts & schemas: machine-readable schemas and validation guidance; the core XSD enforces xs:language on srcLang/trgLang and restores xml:lang constraints for <source>.
• Security/privacy considerations: media type registration and guidance for potentially sensitive constructs (see appendices).
• Normative references: BCP 47, RFCs for media types and IRIs, HTML5, Schematron and related ISO documents.

Applications and Who Uses It

• Localization service providers and translators: for receiving and returning translated segments with context and inline markup preserved.
• CAT tool and TMS developers: to implement imports/exports, translation memory integration and validation against XLIFF schemas.
• Software and content producers (publishers, product teams): to extract UI strings, documentation and web content for localization, then merge translations back.
• Automation and CI/CD localization pipelines: to enable tool-agnostic exchange of multilingual assets and validate translations during builds. Benefits include standardized interchange, reduced manual rework, reliable round-trip merging, and compatible integration with ITS metadata for internationalization.

Related Standards

• ITS 2.0 (W3C Internationalization Tag Set) - native support integrated via the ITS Module
• BCP 47 (language tags), RFC 2119 (requirement keywords), RFC 7303 (XML media types)
• HTML5, Schematron (rule-based validation), ISO/IEC 19757 series (schema/validation technologies)

Keywords: XLIFF, XLIFF 2.0, XML Localization Interchange File Format, localization, interoperability, ITS 2.0, CAT tools, translation, schema validation, segmentation, inline codes.