Fix overlapping issue for Add a language page

As the Add a language page changed its parent class, the collapsing
toolbar did not work smoothly. Also the nested scrolling feature of the
locale list is disabled, that caused the overlapping problem.

This change is to make the locale list enable the nested scrolling
feature.

Fixes: 207318265
Test: manual test
Change-Id: I95929cd569c94d392c325e4e5b2a35e78185d0b8