use text-align smartly (if english dir=ltr if arabic dir=rtl)

You’ll need to create a function that has all the letters you know are RTL and check when loading. To display RTL you need the CSS attributes, direction, text-align, and unicode-bidi.

Demo:

Script

function checkRtl( character ) {
    var RTL = ['ا','ب','پ','ت','س','ج','چ','ح','خ','د','ذ','ر','ز','ژ','س','ش','ص','ض','ط','ظ','ع','غ','ف','ق','ک','گ','ل','م','ن','و','ه','ی'];
    return RTL.indexOf( character ) > -1;
};

var divs = document.getElementsByTagName( 'div' );

for ( var index = 0; index < divs.length; index++ ) {
    if( checkRtl( divs[index].textContent[0] ) ) {
        divs[index].className="rtl";
    } else {
        divs[index].className="ltr";
    };
};

CSS

.rtl {
    direction: rtl; 
    text-align: right;
    unicode-bidi: bidi-override;
}

.ltr {
    direction: ltr; 
    text-align: left;
    unicode-bidi: bidi-override;
}

HTML

<div>hello</div>
<div>ظ</div>