// Before: file I/O blocking the queue, then re-writing same data to disk
let (languagesToSave, callbacks) = queue.sync {
    } else if self._supportedLanguages == nil {
        let cachedData = try? Data(contentsOf: URL(fileURLWithPath: self.filePath)) // ❌ blocking I/O inside queue
        ...
    }
}
saveSupportedLanguages(languages: languagesToSave) // ❌ re-writes data just read from disk on 304

// After: read outside queue, skip write on 304
let needsDiskLoad: Bool = languages == nil && queue.sync { _supportedLanguages == nil }
let diskLanguages = needsDiskLoad ? loadLanguagesFromDisk() : nil // ✅ outside queue
...
if languages != nil {
    saveSupportedLanguages(languages: languagesToSave) // ✅ only on 200
}