Fix a freeze when changing the interface language.

Switching language rebuilt the whole Activity. That saved the game twice, tore
down and rebuilt the audio engine, and waited for the render thread to stop,
all on the main thread, and Android forces pending preference writes to reach
disk before the activity may pause. On slower storage the app could hang for
seconds, sometimes long enough for an "isn't responding" dialog.

The language now changes in place, so the switch is immediate.
