feat(spec): add Icelandic locale support

[devin-ai-integration]

feat(spec): add Icelandic locale support

Summary

Added support for the Icelandic language by adding the is locale code with the is-IS regional variant to the localeMap in packages/spec/src/locales.ts. This change enables Icelandic language support throughout the lingo.dev internationalization system.

The locale system automatically generates various locale format arrays from the base localeMap object, so adding this entry makes Icelandic available across all lingo.dev packages that depend on locale specifications.

Review & Testing Checklist for Human

• Verify locale codes are correct: Confirm that is (Icelandic) and is-IS (Iceland) are the correct ISO 639-1 and BCP 47 codes
• Test end-to-end functionality: Create a test project and verify that Icelandic locale actually works with lingo.dev CLI, compiler, and SDK
• Review changeset configuration: Check that the changeset is properly configured for a minor version bump and will publish correctly
• Validate locale placement: Ensure the placement in localeMap follows the intended organizational pattern

Recommended test plan: Create a simple test project with i18n.json configured for Icelandic (is or is-IS) as a target locale, add some translatable content, and run lingo.dev to verify the locale is recognized and translations work properly.

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    packages["packages/"]
    spec["packages/spec/"]
    locales["packages/spec/src/locales.ts"]:::major-edit
    changeset[".changeset/soft-seals-doubt.md"]:::major-edit
    
    packages --> spec
    spec --> locales
    
    locales --> localeMap["localeMap object"]
    localeMap --> newEntry["+ is: ['is-IS']"]:::major-edit
    
    locales --> exports["Exported arrays"]
    exports --> localeCodesShort["localeCodesShort"]:::context
    exports --> localeCodesFull["localeCodesFull"]:::context
    exports --> localeCodes["localeCodes"]:::context
    
    subgraph Legend
        L1["Major Edit"]:::major-edit
        L2["Minor Edit"]:::minor-edit  
        L3["Context/No Edit"]:::context
    end

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• This change addresses GitHub issue [Language request] Please add Icelandic #994 requesting Icelandic language support
• The locale system generates multiple format variants automatically (underscore delimited, explicit region codes, etc.)
• Build and tests pass successfully, confirming no breaking changes
• Requested by Max Prilutskiy (@maxprilutskiy)
• Link to Devin session: https://app.devin.ai/sessions/f61ed4ced486458891f3d0c06ef679e4

Resolves #994

[devin-ai-integration]

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 6d150d5.

Security Overview

• 🔎 Scanned files: 2 changed file(s)

Detected Code Changes

Change Type	Relevant files
Enhancement	► soft-seals-doubt.md     Add Icelandic locale support ► locales.ts     Add is-IS locale mapping

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[maxprilutskiy]

Suggested change

	"@lingo.dev/_spec": minor
	"@lingo.dev/_spec": patch

[maxprilutskiy]

Resolves #994