Refactor LanguageUtilities to cached LanguageService singleton

[Copilot]

LanguageUtilities created new GlobalLang, WindowsAiLang, and list instances on every call, causing unnecessary memory allocations in hot paths like OCR operations.

Changes

New LanguageService (Text-Grab/Services/LanguageService.cs)

• Caches available OCR languages list on first call
• Caches current input language, invalidates when keyboard language tag changes
• Caches OCR language selection based on LastUsedLang setting
• Caches system translation language string
• Static WindowsAiLang instance reused across calls
• Thread-safe with lock synchronization
• Exposes InvalidateLanguagesCache(), InvalidateOcrLanguageCache(), InvalidateAllCaches() for manual invalidation

Updated LanguageUtilities

• Delegates to Singleton<LanguageService>.Instance
• Full backward compatibility—no call site changes required

// Before: allocates new GlobalLang every call
public static ILanguage GetCurrentInputLanguage()
{
    string inputLang = InputLanguageManager.Current.CurrentInputLanguage.Name;
    return new GlobalLang(inputLang);
}

// After: returns cached instance, only allocates when language changes
public static ILanguage GetCurrentInputLanguage()
    => Singleton<LanguageService>.Instance.GetCurrentInputLanguage();

Tests (Tests/LanguageServiceTests.cs)

• Coverage for GetLanguageTag, GetLanguageKind, singleton behavior, and backward compatibility

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Refactor Language Utilities to be a Service to improve lower string memory allocations for every call</issue_title>
<issue_description>Use a more efficient pattern for querying the languages available. Also cache and query

• Selected Text Grab language and setting
• Keyboard language
• System language</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Refactor Language Utilities to be a Service to improve lower string memory allocations for every call #603

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.