ccn/Packages/Localization/README.md

Localization

The server-side localization toolkit the platform's services build on: locale-explicit String Catalog lookups, Accept-Language negotiation, and the catalog-derived language list — with no dependencies beyond Foundation.

Overview

Role	Types
Lookup	Localize, a bundle-bound localizer that resolves a catalog key for an explicit locale
Negotiation	Negotiate, which picks the best supported language from an explicit request or an Accept-Language header per RFC 9110
Languages	LanguageList, the supported and default languages a bundle's String Catalog defines
Diagnostics	CatalogState, the outcome of reading the catalog (loaded, missing, or undecodable)

Design rules

• The String Catalog is the single source of truth. Supported languages, the default language, and every string come from the bundle's Localizable.xcstrings, so adding a language is a translation-only change.
• The locale is always explicit. A server has no single "current" locale, so every lookup names the locale to resolve in; nothing reads process-wide locale state.
• Raw .xcstrings parsing, for Linux parity. The catalog is decoded from its JSON rather than through Foundation's compiled-catalog APIs, which are unavailable or non-functional on Linux. Consumers must .copy the resource verbatim (never .process it) so it ships as raw JSON everywhere. Only simple stringUnit values are decoded — plural and device variations are not.
• Resolution never fails. A missing entry falls back to the source-language string, then to the key itself; a missing or undecodable catalog degrades the language list to the default. Check catalogState at startup and warn when it is not .loaded.
• Method structs. Localize and Negotiate hold their lifetime-fixed configuration (the bundle) in init and take only per-call inputs in callAsFunction.
• One decoded catalog per bundle. Catalogs are immutable at runtime, so every Localize, Negotiate, and LanguageList bound to the same bundle and table shares one cached StringCatalog.

Layout

Sources are split by visibility, then by kind, one type per file:

Sources/
├── Public/
│   ├── Enumerations/      CatalogState
│   ├── Methods/           Localize, Negotiate
│   └── Types/             LanguageList
└── Internal/
    ├── Protocols/         CatalogResolving, the seam between the public API and the catalog backend
    └── Types/             StringCatalog (the cached .xcstrings decoder), LanguageRange
Tests/
├── Cases/                 the test suites, mirroring the Sources/ layout
├── Catalogs/              the String Catalog fixture, copied verbatim so it loads on Linux
└── Utils/                 the StubCatalog resolver and the suite Tag constants

Testing

Every suite carries a tag for the kind of API it exercises — .method or .type, declared in Tests/Utils/Extensions/Tag+Constants.swift — so test plans and summaries can slice a run by kind. A new suite adopts the tag matching its subject, or adds one when none fits.

Requirements

• Swift 6.3 toolchain (swift-tools-version:6.3).
• macOS 15, matching the sibling packages (the services deploy to Linux containers; the packages carry no UI platforms).
• No package dependencies — Foundation and Synchronization only.