I recommend that you create a JavaScript file called fa.js with the code below in the Lang folder, which is available in the amChart directory.
AmCharts.translations.fa = { "monthNames": ["دی", "بهمن", "اسفند", "فروردین", "اردیبهشت", "خرداد", "تیر", "مرداد", "شهریور", "مهر", "آبان", "آذز"], "shortMonthNames": ["دی", "بهمن", "اسفند", "فروردین", "اردیبهشت", "خرداد", "تیر", "مرداد", "شهریور", "مهر", "آبان", "آذز"], "dayNames": ["یکشنبه", "دوشنبه", "سه شنبه", "چهارشنبه", "پنجشنبه", "جمعه", "شنبه"], "shortDayNames": ["یکشنبه", "دوشنبه", "سه شنبه", "چهارشنبه", "پنجشنبه", "جمعه", "شنبه"], "zoomOutText": "نمایش همه"}
Now you need to do a couple of things more:
Import fa.js into your project
<script type="text/javascript" src="/amcharts/lang/fa.js"></script>
Then define it in the amchart object
var chart = AmCharts.makeChart("chartdiv", { "type": "serial", "theme": "dark", "marginRight": 40, "marginLeft": 40, "language":"fa" . . .