Recursively sort all layers in Illustrator alphabetically

sortLayers.jsx

var deep = true, // Set to false if you don't want to recursively sort layers within layers too
    isLowerFirst = true; // Set it to false if you want to place the layers with the first uppercase letter above

// Convert ILST collection into standard Array so we can use Array methods
function get(type, parent) {
    if (arguments.length == 1 || !parent) parent = app.activeDocument;
    var result = [];
    if (!parent[type]) return result;
    for (var i = 0; i < parent[type].length; i++) result.push(parent[type][i]);
    return result;
}

// Polyfill for Array.forEach
Array.prototype.forEach = function (callback) {
    for (var i = 0; i < this.length; i++) callback(this[i], i, this);
};

function sortLayersInside(parent) {
    function isUpperCase(text) {
        return /[A-Z]/.test(text.charAt(0))
    }
    function isLowerCase(text) {
        return /[a-z]/.test(text.charAt(0))
    }
    function hasMixedCase(a, b) {
        if (a.charAt(0).toLowerCase() !== b.charAt(0).toLowerCase()) return false;
        return isUpperCase(a) && isLowerCase(b) ? true : isLowerCase(a) && isUpperCase(b);
    }
    function handleMixedCase(a, b) {
        var result = a === b ? 0 : isUpperCase(a) ? 1 : -1;
        return isLowerFirst ? result : result * -1;
    }
    get("layers", parent)
        .sort(function (a, b) {
            return hasMixedCase(a.name, b.name) ?
                handleMixedCase(a.name, b.name) :
                a.name.toLowerCase().localeCompare(b.name.toLowerCase())
        })
        .forEach(function (layer) {
            layer.zOrder(ZOrderMethod.SENDTOBACK);
            if (layer.layers && layer.layers.length && deep) sortLayersInside(layer);
        });
}
sortLayersInside();

...Though you can always look at the source code for prototype methods in V8 directly. I'm not sure that this necessarily helps though V8 code tends to have pretty detailed explanations and a walkthrough of what the code is doing via comments.

I manually look at the result of sorting mixed alphabets with .localeCompare() and .toUpperCase(). I didn't check Chinese characters, because I don't know the correct order =)