Add a way for the developer to specify the locale

README.md

@@ -151,6 +151,21 @@ window.barchart_labels = function() {
 }
 ```
 
+### Localize number formatting according to a specific locale
+Wagtail chart formats numbers according to the browser's default locale by default.
+You can override this by setting a global javascript variable called `WAGTAILCHARTS_LOCALE` before calling the `render_charts` template tag:
+
+```django
+{% load wagtailcharts_tags %}
+
+<!-- Your content here -->
+
+{% block extra_js %}
+<script>WAGTAILCHARTS_LOCALE = 'is-IS';</script>
+{% render_charts %}
+{% endblock %}
+```
+
 
 ## Dependencies
 * This project relies on [Jspreadsheet Community Edition](https://bossanova.uk/jspreadsheet/v4/) for data entry and manipulation. 

wagtailcharts/static/wagtailcharts/js/wagtailcharts.js

@@ -3,8 +3,11 @@ var formatValue = function (val, precision = 1, override) {
         return val;
     }
 
-    // Passing 'undefined' for the locale uses the browser's default.
-    number = Intl.NumberFormat(undefined, {maximumFractionDigits: precision}).format(val)
+    // We look for the locale in the window object, which must be set before the `render_charts` template tag is called.
+    // If it is not present, it will be undefined and the browser's default locale will be used.
+    let locale = window.WAGTAILCHARTS_LOCALE;
+
+    number = Intl.NumberFormat(locale, {maximumFractionDigits: precision}).format(val)
 
     if(override !== undefined && override !== "" && override !== null){
         return number + " " + override;