JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cdnjs.cloudflare.com/ajax/libs/xregexp/2.0.0/xregexp-min.js"></script>
<script src="http://xregexp.com/addons/unicode/unicode-base.js"></script>
<script src="http://xregexp.com/addons/unicode/unicode-scripts.js"></script>
<p>Hello World</p>
<p>בײַגל</p>

CSS

p.rtl {
    direction: rtl;
}
p.ltr {
    direction: ltr;
}

JavaScript

$('p').each(function() {
    if(isRTL($(this).text()))
        $(this).addClass('rtl');
});

function isRTL(str) {
    var isHebrew = XRegExp('[\\p{Hebrew}]');
    var isLatin = XRegExp('[\\p{Latin}]');
    var partLatin = 0;
    var partHebrew = 0;
    var rtlIndex = 0;
    var isRTL = false;

    for(i=0;i<str.length;i++){
        if(isLatin.test(str[i]))
            partLatin++;
        if(isHebrew.test(str[i]))
            partHebrew++;
    }
    rtlIndex = partHebrew/(partLatin + partHebrew);
    if(rtlIndex > .5) {
        isRTL = true;
    }
/*
console.log('Latin score: ' + partLatin);
console.log('Hebrew score: ' + partHebrew);
console.log('trlIndex score: ' + rtlIndex);
console.log('isRTL: ' + isRTL);
*/

    return isRTL;
}