It seems like fontFamily attribute doesn't applied if you use japanese string inside a TextView. I've created sample project which shows several TextViews with different fontFamily. Layout is very simple -
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="世界ランキング"
android:fontFamily="sans-serif"
android:textSize="21.33sp"
android:textStyle="normal"
android:textColor="@android:color/black" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="16sp"
android:textStyle="normal"
android:text="sans-serif"
android:fontFamily="sans-serif"
android:textColor="@android:color/black" />
</LinearLayout>
And this is how it looks -
I feel that I'm doing something wrong, please help me to figure out what exactly.