Forgive me to revive this old thread, but it's about the same issue.
My TV is a LE40B551A6W, and exhibits the same absurd behaviour: there are remote buttons to swap subtitles, switch audio description on/off, and none to swap audio language on digital channels.
And then there is, just left of those two buttons, one labelled 'DUAL' that just works on analog channels swapping the old NICAM dual channels (L+R->L->R). On digital channels, it only shows on screen if the audio channel used is stereo or mono. Information only, no change. How useful for a precious piece of remote real state.
According to the Samsung web FAQ, this behaviour is known by Samsung tech service. The official answer is that poor user has to swap languages or audio channels, on digital, by digging into a 5th or 6th level menu. Pressing more than 10 remote keys. Function not even accessible through the quick 'Tools' remote button. But he'll be able to engage subtitles or audio description with only one remote key.
I guess that few people will be surprised to learn that the lucky subtitle option is very typically used along with swapping the audio language to a non default option. In fact, I bet that the audio change is way more often used than the subtitles, not to mention the audio description. How can be justified to assign remote keys to those two, and not to audio channels?
I can't imagine this being a deliberate design decision. It has to be a 'bug', or more appropriately a big overlook. One already detected by hundreds or thousands of perplexed customers.
As the remote limits itself to send keycodes upon keypresses, this behaviour is produced by the TV firmware, which is programmed to react this way when this key is pressed. This bug could be very easily corrected by changing what the FW does when receiving the 'DUAL' keypress when in digital channel, and make it work like the 'SUBTITLE' key do, showing first the current option selected, and next switching to the next available option on next keypress. That's what 99% of the competition TV sets do, and what users expect.
Even other not so older Samsung TV sets do this as I described, but the key is labelled 'ALT'.
There is not even need to change the already documented behaviour when pressing it on analog channels. That's fine, for whoever uses it. In terms of programming it would be a pretty trivial and very low risk change.
I would ask Samsung techies here if there is any reason we could not hope for this being corrected in a new FW version, not much far away in time.
And if not, for which reason.