A simple jQuery plugin to make a input be checked against punctuation, spaces and wrong capitalized words.

human-text.jquery.js

(function ($) {
    $.fn.humanText = function(options) {
        var defaults = {}, settings = {}, app = {};

        /**
         * Array of default settings:
         *
         * - last_mark:      string     The mark to last line. Default is period (.);
         */
        defaults = {
            last_mark: '.',
        };

        settings = $.extend( {}, defaults, options );

        app = {
            original_text: '',
            human_text: '',
            punctuation: [';', '.', '!', '?'],
            ucFirstWord: function() {
                var regex = /([\.|!|?]\s*\w|^\w)/gm;
                app.human_text = app.human_text.replace(regex, function(m, p1) {
                    return p1.substring(0, p1.length - 1) + p1.substring(p1.length - 1).toUpperCase();
                });
            },
            removeSpaceBeforeParagraph: function() {
                var regex = /^[ ]+(\w)/gm;
                app.human_text = app.human_text.replace(regex, function(m, p1) { return p1; });
            },
            addPunctuation: function() {
                var regex = /([^?|!|\.|;|\s])$/gm;

                if (app.punctuation.indexOf(app.human_text.charAt(app.human_text.length - 1)) < 0) {
                    app.human_text += settings.last_mark;
                }

                app.human_text = app.human_text.replace(regex, function(m, p1) { return p1 + '.'; });
            },
            addSpaceAfterPunctuation: function() {
                var regex = /([^A-Z\u00C0-\u00DD]{1}[?|!|\.|;]+)([^ \n\.?!]{1})|([A-Z\u00C0-\u00DD][?|!|\.|;|,|:]+)([a-z\u00E1-\u00F6\u00F9-\u00FD]+)/g;

                app.human_text = app.human_text.replace(regex, function(m, p1, p2, p3, p4) {
                    if (typeof p1 == 'undefined') {
                        p1 = p3;
                        p2 = p4;
                    }

                    return p1 + ' ' + p2;
                });
            },
            trimAtEnd: function() {
                app.human_text = app.human_text.trim();
            },
            toLowerCase: function() {
                var regex1 = /(\b[a-z\u00E1-\u00F6\u00F9-\u00FD]{1}[A-Z\u00C0-\u00DD]{2,}\b)/g,
                    regex2 = /(\b[A-Z\u00C0-\u00DD]+[a-z\u00E1-\u00F6\u00F9-\u00FD]+[A-Z\u00C0-\u00DD]+[A-Z\u00C0-\u00DDa-z\u00E1-\u00F6\u00F9-\u00FD]*\b)/g,
                    regex3 = /(\b[a-z\u00E1-\u00F6\u00F9-\u00FD]+[A-Z\u00C0-\u00DD]+[a-z\u00E1-\u00F6\u00F9-\u00FD]+[a-z\u00E1-\u00F6\u00F9-\u00FDA-Z\u00C0-\u00DD]*\b)/g,
                    regex4 = /((?:\b[A-Z\u00C0-\u00DD]+\b[ ]+\b)+[A-Z\u00C0-\u00DD]+\b)/g;

                app.human_text = app.human_text.replace(regex1, function(m, p1) { return p1.charAt(0).toUpperCase() + p1.slice(1).toLowerCase(); });
                app.human_text = app.human_text.replace(regex2, function(m, p1) { return p1.toLowerCase(); });
                app.human_text = app.human_text.replace(regex3, function(m, p1) { return p1.toLowerCase(); });
                app.human_text = app.human_text.replace(regex4, function(m, p1) { return p1.toLowerCase(); });
            },
            applyText: function(el, event_type) {
                var caret = 0, distance = 0;

                if (event_type != 'keyup') {
                    el.val(app.human_text);
                    return;
                }

                caret = app.getCaret(el.get(0));
                el.val(app.human_text);

                if ( typeof caret == 'object' && typeof caret.end == 'number' ) {
                    distance = app.original_text.length - caret.end;
                    distance = app.human_text.length - distance;

                    app.moveCaret(el.get(0), distance);
                }
            },
            getCaret: function(el) {
                var start = 0, end = 0, normalizedValue, range,
                    textInputRange, len, endRange;

                if (typeof el.selectionStart == "number" && typeof el.selectionEnd == "number") {
                    start = el.selectionStart;
                    end = el.selectionEnd;
                } else if (typeof document.selection != 'undefined') { // IE < 9
                    range = document.selection.createRange();

                    if (range && range.parentElement() == el) {
                        len = el.value.length;
                        normalizedValue = el.value.replace(/\r\n/g, "\n");

                        // Create a working TextRange that lives only in the input
                        textInputRange = el.createTextRange();
                        textInputRange.moveToBookmark(range.getBookmark());

                        // Check if the start and end of the selection are at the very end
                        // of the input, since moveStart/moveEnd doesn't return what we want
                        // in those cases
                        endRange = el.createTextRange();
                        endRange.collapse(false);

                        if (textInputRange.compareEndPoints("StartToEnd", endRange) > -1) {
                            start = end = len;
                        } else {
                            start = -textInputRange.moveStart("character", -len);
                            start += normalizedValue.slice(0, start).split("\n").length - 1;

                            if (textInputRange.compareEndPoints("EndToEnd", endRange) > -1) {
                                end = len;
                            } else {
                                end = -textInputRange.moveEnd("character", -len);
                                end += normalizedValue.slice(0, end).split("\n").length - 1;
                            }
                        }
                    }
                }

                return {
                    start: start,
                    end: end
                };
            },
            moveCaret: function(input, distance) {
                if (input.setSelectionRange) {
                    input.focus();
                    input.setSelectionRange(distance, distance);
                } else if(input.createTextRange) {
                    var range = input.createTextRange();
                    range.collapse(true);
                    range.moveEnd(distance);
                    range.moveStart(distance);
                    range.select();
                }
            }
        };

        this.filter('input, textarea').each(function () {
            $(this).on('apply_human_text', function(event, event_type) {
                var input = $(this);

                app.original_text = input.val();
                app.human_text = app.original_text;

                // Return if empty
                if (app.original_text == '') {
                    return;
                }

                if (event_type == 'change') {
                    // Remove space at end
                    app.trimAtEnd();

                    // If empty, apply the new empty text and finish
                    if (app.human_text == '') {
                        app.applyText(input, event_type);
                        return;
                    }

                    // Add a dot at end of each line (a question mark to the last one) if there is none.
                    app.addPunctuation();

                    // Add space after each punctuation ignoring A.B.R.E.V.I.A.T.I.O.N.S
                    app.addSpaceAfterPunctuation();
                }

                // Make string be lowercase if:
                // Regex 1: A lone word is a wrong cAPITALIZED word (became Capitalized)
                // Regex 2: A lone word is a wrong CApItalizeD/CApItalized word (became capitalized)
                // Regex 3: A lone word is a wrong cApItAliZEd/cApItAliZED word (became capitalized)
                // Regex 4: Two (or more) adjacent words are CAPITALIZED
                app.toLowerCase();


                // Make the first letter of each first word capitalized:
                // In each start of line or when there's a punctuation before
                app.ucFirstWord();

                // Remove spaces in start of each line
                app.removeSpaceBeforeParagraph();

                // Return if nothing changed
                if (app.original_text == app.human_text) { return; }

                // Apply the new text
                app.applyText(input, event_type);
            });

            $(this).on('keyup change', function(event) {
                $(this).trigger('apply_human_text', event.type);
            });
        });

        return this;
    }
}(jQuery));