[PM-26060] Create LanguageStateService in BWK

[KatherineInCode]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-26060

📔 Objective

This segregates out some of the StateService interface into a LanguageStateService, providing a common definition and finer granularity for working with the apps' language selections.

I elected to make this change separate from bringing the whole Select Language UX in to make for smaller PRs in general.

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[github-actions]

Checkmarx One – Scan Summary & Details – c68087a4-f0fc-4598-bde6-74ba1e64bcd4

Great job! No new security vulnerabilities introduced in this pull request

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.94%. Comparing base (98ee2b6) to head (bad742b).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...ared/Core/Platform/Services/ServiceContainer.swift	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2148      +/-   ##
==========================================
- Coverage   85.39%   83.94%   -1.46%     
==========================================
  Files        1721     1978     +257     
  Lines      145463   160942   +15479     
==========================================
+ Hits       124224   135102   +10878     
- Misses      21239    25840    +4601     

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[claude]

Claude finished @KatherineInCode's task —— View job

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Code Review Complete

Summary

This PR successfully extracts language state management from StateService into a dedicated LanguageStateService protocol in BitwardenKit. The implementation follows established architectural patterns, properly uses dependency injection, and includes comprehensive test updates. The change provides better granularity and interface segregation.

Key Changes:

• Created new LanguageStateService protocol in BitwardenKit with single responsibility for language state (BitwardenKit/Core/Platform/Services/LanguageStateService.swift:1)
• DefaultStateService now conforms to LanguageStateService in both apps
• Updated SelectLanguageProcessor in both apps to depend on LanguageStateService instead of full StateService
• Properly integrated into ServiceContainer with dependency injection
• Updated all tests to use MockLanguageStateService

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Findings

Finding 1: Missing DocC documentation on protocol property

Details

The LanguageStateService protocol in BitwardenKit/Core/Platform/Services/LanguageStateService.swift:1-5 follows the .claude/CLAUDE.md guideline that protocol properties should have DocC documentation (implementations inherit from protocol). The protocol-level documentation is present and properly formatted. ✅

No issue found - documentation is correct as-is.

Finding 2: Review comment addressed

Details

The review comment from @matt-livefront about moving HasLanguageStateService to the centralized Services.swift file has been properly addressed. The protocol is now in BitwardenKit/Core/Platform/Services/Services.swift:38-43, consistent with other Has<Service> protocols. ✅

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Architecture & Design Review

✅ Follows established patterns: The implementation correctly follows the dependency injection pattern described in Docs/Architecture.md
✅ Interface segregation: Properly segregates language state concerns from the broader StateService
✅ Protocol composition: Correctly uses Has<Service> pattern for dependency injection
✅ Target boundaries: Changes appropriately span BitwardenKit, BitwardenShared, and AuthenticatorShared
✅ Actor isolation: DefaultStateService implementations correctly use nonisolated for the appLanguage property since it accesses thread-safe stores

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Code Quality

✅ Documentation: Protocol and implementations properly documented following DocC standards
✅ Naming: Clear, descriptive names following Swift conventions
✅ Dependencies: Properly uses ServiceContainer for DI
✅ Test coverage: All processor tests updated to use new service type
✅ Mock generation: Protocol correctly annotated with // sourcery: AutoMockable

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Test Coverage Analysis

Updated Tests:

• SelectLanguageProcessorTests (both apps): ✅ Updated to use MockLanguageStateService
• ServiceContainer+Mocks (both apps): ✅ Added languageStateService parameter with default mock

Test Pattern Compliance:

• ✅ Tests properly use mocks for isolation
• ✅ Tests verify state changes and service interactions
• ✅ setUp/tearDown properly manage test lifecycle

Codecov Report: 93.75% patch coverage with 1 missing line in AuthenticatorShared ServiceContainer (likely a non-critical initialization path).

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Security Considerations

✅ No security concerns identified. Language selection is a benign user preference that doesn't involve sensitive data or authentication flows.

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Good Practices Observed

• Clean interface segregation following SOLID principles
• Consistent implementation across both Password Manager and Authenticator apps
• Proper use of protocol composition for dependency management
• nonisolated correctly applied for actor-isolated property access

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Action Items

None. This PR is ready to merge. All requirements have been met:

• ✅ Architecture guidelines followed
• ✅ Code style compliant
• ✅ Tests updated and passing (linting passed, other CI checks in progress)
• ✅ Documentation complete
• ✅ Review comments addressed

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