Cute Numbers with spaces. Cyrillic labels by last number.

cuteNumbers.js

function cuteNumber(num) {
    num = ''+num;
    return num.replace(/(\d)(?=(\d\d\d)+([^\d]|$))/g, '$1 ');;
}

function cuteNumberObjects(num, replacer = ['объект', 'объекта', 'объектов']) {
    num = cuteNumber(num);

    switch(num[num.length - 1]) {
        case '1':
            return `${num} ${replacer[0]}`;
        case '2' || '3' || '4':
            return `${num} ${replacer[1]}`;
        case '0' || '5' || '6' || '7' || '8' || '9':
            return `${num} ${replacer[2]}`;
    }
}

console.log(cuteNumberObjects(5421, ['картинка', 'картинки', 'картинок']));