A android.widget.Switch that accepts the attribute "android:fontFamily" inside a style defined by the attribute "android:switchTextAppearance". Makes sense from API 16+ as before the attribute doesn't exist; however it can easily be modified with a custom one.

attrs.xml

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <declare-styleable name="Android">
        <attr name="android:fontFamily"/>
    </declare-styleable>

</resources>

layout_example.xml

<?xml version="1.0" encoding="utf-8"?>

<SwitchFamilyName
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    style="@style/Switch"/>

style_example.xml

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <style name="Switch">
        <item name="android:switchTextAppearance">@style/Switch.SwitchTextAppearance</item>
    </style>

    <style name="Switch.SwitchTextAppearance" parent="Switch">
        <item name="android:fontFamily">sans-serif-condensed</item>
    </style>

</resources>

SwitchFamilyName.java

package android.widget;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.widget.Switch;

/**
 * 28/12/13
 * Created by Eugenio Marletti
 * https://gist.github.com/Takhion/8197815
 */

/**
 * A Switch that accepts the attribute "android:fontFamily" inside a style defined by the
 * attribute "android:switchTextAppearance".
 *
 * @attr ref android.R.styleable#TextView_fontFamily
 * @attr ref android.R.styleable#Switch_switchTextAppearance
 */
@TargetApi(16)
public final class SwitchFamilyName extends Switch
{
    /**
     * Construct a new Switch with default styling.
     *
     * @param context The Context that will determine this widget's theming.
     */
    public SwitchFamilyName(Context context)
    {
        super(context);
    }

    /**
     * Construct a new Switch with default styling, overriding specific style
     * attributes as requested.
     *
     * @param context The Context that will determine this widget's theming.
     * @param attrs   Specification of attributes that should deviate from default styling.
     */
    public SwitchFamilyName(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }

    /**
     * Construct a new Switch with a default style determined by the given theme attribute,
     * overriding specific style attributes as requested.
     *
     * @param context  The Context that will determine this widget's theming.
     * @param attrs    Specification of attributes that should deviate from the default styling.
     * @param defStyle An attribute ID within the active theme containing a reference to the
     *                 default style for this widget. e.g. android.R.attr.switchStyle.
     */
    public SwitchFamilyName(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
    }

    /**
     * Sets the switch text color, size, style, font family, hint color, and
     * highlight color from the specified TextAppearance resource.
     *
     * @attr ref android.R.styleable#Switch_switchTextAppearance
     */
    @Override
    public void setSwitchTextAppearance(Context context, int resid)
    {
        super.setSwitchTextAppearance(context, resid);

        TypedArray appearance = null;
        try
        {
            appearance = context.obtainStyledAttributes(resid, R.styleable.Android);
            final String fontFamily = appearance.getString(R.styleable.Android_android_fontFamily);
            if (fontFamily != null)
            {
                final Typeface currentTypeface = getTypeface();
                final Typeface newTypeface = Typeface.create(fontFamily, currentTypeface != null
                                                                         ? getTypeface().getStyle() : Typeface.NORMAL);
                if (newTypeface != null) setSwitchTypeface(newTypeface);
            }
        }
        finally
        {
            if (appearance != null) appearance.recycle();
        }
    }
}