Which layouts and images mirror for right-to-left languages automatically, and what must you handle yourself in custom drawing?

Predict first

Where do cells land in a mirrored flow layout, and which images flip?

import UIKit

final class DS: NSObject, UICollectionViewDataSource {
    func collectionView(_ c: UICollectionView, numberOfItemsInSection s: Int) -> Int { 2 }
    func collectionView(_ c: UICollectionView, cellForItemAt i: IndexPath) -> UICollectionViewCell { c.dequeueReusableCell(withReuseIdentifier: "c", for: i) }
}
@MainActor func run() {
    let v = UIView(); v.semanticContentAttribute = .forceRightToLeft
    print("direction raw (0 ltr, 1 rtl):", v.effectiveUserInterfaceLayoutDirection.rawValue,
          UIView.userInterfaceLayoutDirection(for: .forceRightToLeft).rawValue,
          UIView.userInterfaceLayoutDirection(for: .playback).rawValue,
          UIView.userInterfaceLayoutDirection(for: .spatial).rawValue)
    let layout = UICollectionViewFlowLayout(); layout.itemSize = CGSize(width: 100, height: 50)
    let cv = UICollectionView(frame: CGRect(x: 0, y: 0, width: 320, height: 200), collectionViewLayout: layout)
    let ds = DS()
    cv.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "c"); cv.dataSource = ds
    for attr in [UISemanticContentAttribute.forceLeftToRight, .forceRightToLeft] {
        cv.semanticContentAttribute = attr
        cv.reloadData(); cv.layoutIfNeeded()
        let x = (0..<2).map { layout.layoutAttributesForItem(at: IndexPath(item: $0, section: 0))!.frame.origin.x }
        print(attr == .forceRightToLeft ? "rtl" : "ltr", "item x:", x)
    }
    let chevron = UIImage(systemName: "chevron.right")!, star = UIImage(systemName: "star")!
    print("flips: chevron", chevron.flipsForRightToLeftLayoutDirection, "star", star.flipsForRightToLeftLayoutDirection, "after flipped copy:", chevron.imageFlippedForRightToLeftLayoutDirection().flipsForRightToLeftLayoutDirection)
}
MainActor.assumeIsolated { run() }

• direction raw: 1 1 0 0 / ltr item x: [0.0, 110.0] / rtl item x: [220.0, 110.0] / flips: chevron false star false after flipped copy: true
• rtl item x: [0.0, 110.0]
• chevron true star true