Two way light switch

One way

N L
| |
| \----------\
| /--------\ |
| |        | |
\ /        | |
 X         12C

Two way

In all cases I've wired the switches so that when they are both in the off (L2) position the light is off.

Naive

An issue here is unidirectional current that can cause interference in electronics.

N L
| |
| \-------------------\
| /----------\        |
| |          |        |
\ /          |        |
 X         12C        C12
           ||          ||
           |\----------/|
           \------------/

N L
| |
| \-------------------\
| /----------\        |
| |          |        |
\ /          |        |
 X         12C        C12
           |            |
           |            |
           \------------/

N L
| |
| \-------------------\
| /----------\        |
| |          |        |
\ /          |        |
 X         12C        C12
            |          |
            \----------/

Correct

Whenever current flows in a cable, it does so in two conductors in opposite directions.

N L
| |
| \---------T-----------\
| /--------T+----------\|
| |        ||/--------\||
\ /        |||        |||
 X         12C        C12

N L
| |
| \---------------------\
| /--------\            |
| |        | /--------\ |
\ /        | |        | |
 X         12C        C12

N L
| |
| \---------\
| /---------+----------\
| |         |/--------\|
\ /         ||        ||
 X         12C        C12