A simple Auto Layout solution for a UIButton with 2 labels.

TwoLabelButton.swift

class CustomButton: UIButton {
    
    internal required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    internal override init(frame: CGRect) {
        super.init(frame: frame)
    }
}

class TwoLabelButton: CustomButton {
    
    public let lhsTextLabel = UILabel(frame: .zero)
    public let rhsTextLabel = UILabel(frame: .zero)
    
    override var contentEdgeInsets: UIEdgeInsets {
        
        didSet {
            self.setNeedsLayout()
        }
    }
    
    convenience init() {
        
        self.init(frame: .zero)
        
        self.addSubview(self.lhsTextLabel)
        self.addSubview(self.rhsTextLabel)
        
        self.lhsTextLabel.translatesAutoresizingMaskIntoConstraints = false
        self.rhsTextLabel.translatesAutoresizingMaskIntoConstraints = false
    }
    
    override func layoutSubviews() {
        
        super.layoutSubviews()
        
        let lhsCenterV = NSLayoutConstraint(item: self.lhsTextLabel,
                                            attribute: .centerY,
                                            relatedBy: .equal,
                                            toItem: self,
                                            attribute: .centerY,
                                            multiplier: 1.0,
                                            constant: 0.0)
        
        let rhsCenterV = NSLayoutConstraint(item: self.rhsTextLabel,
                                            attribute: .centerY,
                                            relatedBy: .equal,
                                            toItem: self,
                                            attribute: .centerY,
                                            multiplier: 1.0,
                                            constant: 0.0)
        
        let lhsLeading = NSLayoutConstraint(item: self.lhsTextLabel,
                                            attribute: .leadingMargin,
                                            relatedBy: .equal,
                                            toItem: self,
                                            attribute: .leadingMargin,
                                            multiplier: 1.0,
                                            constant: self.contentEdgeInsets.left)
        
        let rhsTrailing = NSLayoutConstraint(item: self.rhsTextLabel,
                                             attribute: .trailingMargin,
                                             relatedBy: .equal,
                                             toItem: self,
                                             attribute: .trailingMargin,
                                             multiplier: 1.0,
                                             constant: -self.contentEdgeInsets.right)
        
        self.addConstraints([lhsCenterV, lhsLeading, rhsCenterV, rhsTrailing])
    }
    
    // MARK: - Convenience
    
    public func setTitles(_ titleStrings: (String?, String?) = (nil, nil)) {
    
        self.lhsTextLabel.text = titleStrings.0
        self.rhsTextLabel.text = titleStrings.1
    }
}