There is an answer to the similar question.
http://forum.tp-link.com/showthread.php?79585-Obtaining-channel-14&highlight=japan

Channel 14 is only for 11b mode in Japan. No need to use channel 14...It is helpless...Believe me.

I chose the mode (b) only and region japan but i don't see channel 14 ????????????????????????

Hi @MOH

I think their products have not yet been sold in Japan..so ch14 is not opened in the driver..

And i agree with @fotodamaris, The key point is why you want to use channel 14? (11b is really old and useless, and channel 14 is not as good as you expect)

Just post your scenario and requirements so that other users can help.;)

Scenario is as follows:
I want to use channel 14 to move away from the confusion and overlap in the channels.

1- Access Point (7210). Bridge bridge with access point also 7210 .
This scenario is currently applied on channel 13 but I want to use channel 14

Good job to add this technique i like that same airmax from ubiquti
i upgraded this firmware i will test the devices but i don't see channel 14 after upgrade

Thank all! This advice will come in handy.