Accessibility & Localization

How it works — accessibility

• Label = what it is (“Volume” — never “Volume button”, the trait says button). Value = current state (“70%”). Traits = role/state (.button .header .selected .adjustable .notEnabled). Hint = result of acting, spoken last, user can turn hints off.
• isAccessibilityElement = true makes a view a leaf; on a container it hides the children. Order children with accessibilityElements = [...]. Decorative: .accessibilityHidden(true).
• Grouping (SwiftUI): .accessibilityElement(children:) .combine (one swipe, merged) · .ignore (you label it) · .contain (keep children, group them).
• .adjustable needs accessibilityIncrement()/ Decrement() (SwiftUI .accessibilityAdjustableAction).
• Custom actions (UIAccessibilityCustomAction, .accessibilityAction(named:)) expose swipe/long-press actions via the Actions rotor; custom rotors (.accessibilityRotor) jump between headings/links. Announce: UIAccessibility.post(notification: .announcement, …).
• accessibilityIdentifier is for UI tests: stable, not localized, never spoken.
• Dynamic Type: UIFont.preferredFont(forTextStyle:) or UIFontMetrics(forTextStyle:).scaledFont(for:) + adjustsFontForContentSizeCategory = true (default false) + numberOfLines = 0. SwiftUI text styles scale by themselves; @ScaledMetric. AX sizes → stack vertically.
• Settings: Reduce Motion (\.accessibilityReduceMotion: swap zoom for fades), Reduce Transparency, Increase Contrast, Bold Text. Contrast ≥ 4.5:1 (3:1 large text); never colour alone.
• Targets ≥ 44×44 pt. Audit: Accessibility Inspector + XCUIApplication().performAccessibilityAudit() (iOS 17).

How it works — localization

• String Catalog .xcstrings (Xcode 15, JSON): keys extracted at build, per-language state, plural + device variants inline. Replaces .strings + .stringsdict.
• Code: String(localized: "key", defaultValue:, comment:) (iOS 15), LocalizedStringResource; SwiftUI Text("literal") is a LocalizedStringKey. Packages: bundle: .module. Always a comment:.
• Plurals: “Vary by plural” — categories zero one two few many other per language (Polish: one / few / many). Never count == 1 ? :.
• RTL: leading/trailing + .natural alignment mirror; left/right never do. Opt out per view with semanticContentAttribute (.playback for media controls); SwiftUI \.layoutDirection.
• Formatters: date.formatted(…), .currency(code:), Measurement (km↔mi). Locale.current = format region, not UI language.
• Test: pseudolanguages (Accented, Bounded, Double-Length, RTL); vendors get Export Localizations (.xcloc/XLIFF).

Example

HStack {                           // a volume row
  Image(systemName: "speaker.wave.2").accessibilityHidden(true)
  Text("Volume")                   // LocalizedStringKey
  Slider(value: $level)
}
.accessibilityElement(children: .ignore)
.accessibilityLabel("Volume")      // no "slider" - trait adds it
.accessibilityValue(Text(level, format: .percent))
.accessibilityAdjustableAction {   // swipe up / down
  level += $0 == .increment ? 0.1 : -0.1 }
.accessibilityIdentifier("settings.volume")   // tests only
// catalog key "%lld files deleted", varied by plural
let msg = String(localized: "\(count) files deleted",
                 comment: "Toast after bulk delete")

Picture — what VoiceOver says

Picture — positional arguments & mirroring

Interview traps

• “Play button” as label → “Play button, button”.
• isAccessibilityElement on a container hides its children.
• preferredFont without the adjustsFont… flag → never re-scales.
• UI tests matching localized labels — use accessibilityIdentifier.
• "\(n) " + "items" — breaks word order and plurals.
• Text(aStringVar) is not localized — only literals / keys.

Remember

“L-V-T-H” — Label, Value, Trait, Hint (the order VoiceOver speaks). Localize sentences, not words; lead, don’t left.

Likely questions

1. Label vs identifier? — spoken + localized vs silent test hook.
2. Scale a custom font? — UIFontMetrics scaledFont(for:).
3. Why %1$@? — lets translators reorder arguments.
4. Catch truncation / hard-coded text early? — pseudolanguages.
5. Swipe-to-delete for VoiceOver? — accessibility custom action.