Changing Actionbar title font is not completely supported, but you can use a custom view for your action bar. Use custom view and disable native title. It will display between icon and action items. You can inherit all activities from a single activity, which has this code in onCreate:
this.getActionBar().setDisplayShowCustomEnabled(true);
this.getActionBar().setDisplayShowTitleEnabled(false);
LayoutInflater inflator = LayoutInflater.from(this);
View v = inflator.inflate(R.layout.customTitleView, null);
//you can customise anything about the text here.
//Using a custom TextView with a custom font in layout xml so all you need to do is set title
((TextView)v.findViewById(R.id.title)).setText(this.getTitle());
//assign the view to the actionbar
this.getActionBar().setCustomView(v);
and your layout xml (R.layout.customTitleView in the code above) looks like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/transparent" >
<com.your.package.CustomTextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginLeft="10dp"
android:textSize="20dp"
android:maxLines="1"
android:ellipsize="end"
android:text="" />
</LinearLayout>