Expand localization support to the requested locale set

[leynos]

Summary

Expand Netsuke's Fluent localization support to the following requested locale
set in one coordinated change:

• ar
• cs
• cy
• da
• de
• el
• en-GB
• es-419
• es-ES (already present; audit and retain)
• fa
• fi
• fr
• gd
• he
• hi
• hu
• id
• it
• ja
• ko
• nb
• nl
• pl
• pt-BR
• pt-PT
• ro
• ru
• sv
• th
• tr
• uk
• vi
• zh-Hans
• zh-Hant

en-US remains the source and fallback locale. es-ES already exists, so the
net addition is 33 locale catalogues.

Current state

• Cargo.toml declares only en-US and es-ES.
• src/cli_localization.rs embeds those two resources and dispatches every
  Spanish language tag to es-ES.
• build_l10n_audit.rs hard-codes the two catalogue paths.
• Tests and release-help paths contain several two-locale or en-US-specific
  assumptions.

Proposed work

• Add complete Fluent catalogues under locales/<locale>/messages.ftl for all
  requested tags, retaining key names and variables from en-US.
• Replace language-only dispatch with exact locale matching plus deliberate
  fallback rules, so es-419 and es-ES, pt-BR and pt-PT, and
  zh-Hans and zh-Hant remain distinct.
• Make the build-time localization audit validate every declared locale rather
  than hard-coding two paths. Keep one authoritative locale registry shared by
  embedding, validation, metadata, and tests, or document why those surfaces
  cannot share it.
• Update OrthoConfig metadata, rerun-if-changed declarations, CLI/runtime locale
  resolution, help generation, packaging, and relevant release paths.
• Add parameterized unit and behavioural coverage for exact selection,
  language/region/script fallback, unsupported-locale fallback to en-US,
  Unicode rendering, interpolation variables, and CLDR plural categories.
• Add bidirectional/RTL smoke coverage for ar, fa, and he; ensure output
  code does not insert direction-breaking assumptions.
• Update docs/translators-guide.md, docs/users-guide.md,
  docs/netsuke-design.md, and docs/contents.md with the registry ownership,
  fallback policy, and translator workflow.

Translation quality

Machine-generated or copied English catalogues are not completion. Each locale
must be reviewed for terminology, Fluent syntax, interpolation variables,
plural rules, punctuation, and script/region appropriateness. Catalogue review
can be staged internally, but this issue is complete only when all requested
locales meet the same validation contract.

Acceptance criteria

• All 34 requested locale tags are selectable, with en-US retained as
  the source/fallback locale.
• All 33 new catalogues are complete and es-ES is audited against the
  current en-US key set.
• Exact region/script variants are not collapsed into a generic language
  mapping.
• The build-time audit discovers or iterates every declared locale and
  rejects missing keys, orphaned keys, and variable mismatches.
• Parameterized tests cover every locale plus representative plural,
  interpolation, Unicode, and RTL behaviour.
• Packaging includes every catalogue and generated help paths follow the
  documented locale policy.
• Translator and user documentation list all supported locales and explain
  fallback behaviour.
• make check-fmt, make lint, make test, make markdownlint, and
  make nixie pass.

References

• locales/
• Cargo.toml (package.metadata.ortho_config.locales)
• src/cli_localization.rs
• src/locale_resolution.rs
• build.rs
• build_l10n_audit.rs
• docs/translators-guide.md

[coderabbitai]

🔗 Related PRs

leynos/theoremc#9 - Localization proposal [closed]
leynos/corbusier-mockup#8 - Settings and global pages [closed]
#326 - Snapshot localized CLI help output (#290) [open]
leynos/whitaker#277 - Enforce Oxford spelling with Typos [merged]
#427 - Align v0.1.0 documentation and test every example [merged]

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