Tk Source Code

Tk does not support screen readers on any platform.

Accessibility is actually a huge topic. It requires a large implementation across three different API's (Apple's NSAccessability API, Windows' MSAA, and AT-SPI on Unix). It would take hundreds of hours at a minimum to implement and test even a basic implementation for Tk: this would easily be the largest addition to Tk since the themed Tk widgets, which came 10 years ago. 

This is one area where Tk is sorely lacking; most other cross-platform toolkits (Java and Qt, in particular) support accessibility. However, the resources required to implement this in Tk are enormous, and it is not surprising that no one has stepped forward to take on the task. 

If you have immediate needs, you are probably better off choosing another toolkit for your project.