Don't try to load non-existent English locale file

AKPlan/templates/AKPlan/plan_akslot.html

@@ -7,7 +7,10 @@
 <link href='{% static 'AKPlan/vendor/fullcalendar-scheduler/main.css' %}' rel='stylesheet'/>
 
 {% with 'AKPlan/vendor/fullcalendar-scheduler/locales/'|add:LANGUAGE_CODE|add:'.js' as locale_file %}
-    <script src="{% static locale_file %}"></script>
+    {% if LANGUAGE_CODE != "en" %}
+        {# Locale 'en' is included in main.js and does not exist separately #}
+        <script src="{% static locale_file %}"></script>
+    {% endif %}
 {% endwith %}
 
 <script>

AKPlan/templates/AKPlan/plan_base.html

@@ -16,7 +16,10 @@
     <link href='{% static 'AKPlan/vendor/fullcalendar-scheduler/main.css' %}' rel='stylesheet'/>
 
     {% with 'AKPlan/vendor/fullcalendar-scheduler/locales/'|add:LANGUAGE_CODE|add:'.js' as locale_file %}
-        <script src="{% static locale_file %}"></script>
+        {% if LANGUAGE_CODE != "en" %}
+            {# Locale 'en' is included in main.js and does not exist separately #}
+            <script src="{% static locale_file %}"></script>
+        {% endif %}
     {% endwith %}
 
     {% block fullcalendar %}{% endblock %}

AKPlan/templates/AKPlan/plan_wall.html

@@ -25,7 +25,10 @@
     <link href='{% static 'AKPlan/vendor/fullcalendar-scheduler/main.css' %}' rel='stylesheet'/>
 
     {% with 'AKPlan/vendor/fullcalendar-scheduler/locales/'|add:LANGUAGE_CODE|add:'.js' as locale_file %}
-        <script src="{% static locale_file %}"></script>
+        {% if LANGUAGE_CODE != "en" %}
+            {# Locale 'en' is included in main.js and does not exist separately #}
+            <script src="{% static locale_file %}"></script>
+        {% endif %}
     {% endwith %}
 
     <script>

AKScheduling/templates/admin/AKScheduling/scheduling.html

@@ -17,7 +17,10 @@
     <link href='{% static 'AKPlan/vendor/fullcalendar-scheduler/main.css' %}' rel='stylesheet'/>
 
     {% with 'AKPlan/vendor/fullcalendar-scheduler/locales/'|add:LANGUAGE_CODE|add:'.js' as locale_file %}
-        <script src="{% static locale_file %}"></script>
+        {% if LANGUAGE_CODE != "en" %}
+            {# Locale 'en' is included in main.js and does not exist separately #}
+            <script src="{% static locale_file %}"></script>
+        {% endif %}
     {% endwith %}
 
     <style>