Three modes available:

"0" – LTR user interface, no switch available
"1" – RTL user interface, user can switch to LTR
"2" – LTR user interface, user can switch to RTL

Basically:

— Set to "1" if your language requires RTL user interface
— Set to "0" otherwise

"2" is reserved for an unlikely case when language is RTL, but it turns out users (statistically) prefer LTR user interface.

This value affects layout direction on all screens and never displayed as a string directly.

LTR means Left-to-Right
RTL means Right-to-Left