I have seen things about game accessibility guidelines before. Some are good ideas I think, some are not applicable or not appropriate for some games I think, etc. Also, it is not only about disabilities but also much about preferences and better design in general.

Having separate volume controls for music and sound effects is good idea. (You can then also turn them off entirely if you don't want them, by setting the volume level to zero.) For DOS games using PC speaker (or other systems without volume controls), simply allowing to toggle music/sound separately can help (if you are using DOSBOX emulator, then the MIXER command can be used for volume controls).

Allowing controls to be remapped is good idea. (If you design for an older system which is emulated, then usually the emulator will allow remapping controls, as well as other things (including to avoid malware, having zoom setting, etc)

For difficulty setting, ensure that the hardest level is not too easy; it is too common to find the hard mode is made too easy. They mention making the game easier; what is needed is option to making the game more difficult.

"Many games have a training-modus which may be all that is required for some users to be able to use the program." Yes and I don't like that; I don't really like the training mode so much and I think that describing all of the rules in precise detail in the instruction book is much better.

I dislike inline tutorials and think that separate documentation is better. I don't want it to always display help and stuff; I can read the document separately. (Having it a user-configurable option can help.)

"Use explicit visual/audio rewards" Actually I don't want to see so many animations and videos and stuff

"Easy installation, preferably without changing system files" A very good idea, if possible.

"It should be possible to repeat speech messages" If captions are available then they can be displayed as text as well. For messages displayed as text (including the captions of the speech), having a message history menu to view previous messages can be helpful. Some computer games have this. Some don't (although it is a feature I have added to FreeZZT). I have yet to see any television set that can do this with the captions.

Television captions are not only for hard of hearing; many people use it, I use it myself even though I can hear it too.

"Deactivate special keys/functions" It should be an option, not mandatory. Some users may wish to keep them activated, due to continuing to use them.

About having keyboard controls, it was mentioned to me on the IRC, relating to Free Hero Mesh. I had designed Free Hero Mesh at first it uses keyboard controls for nearly everything, although functions requiring coordinate selection use the mouse only. Due to the suggestion though, I have now added the possibility of coordinate selection by keyboard too (the $key_xy SQL parameter can be used in a key binding definition to activate this function). (The original Hero Hearts software required the mouse for many functions; I dislike that so made most of it keyboard oriented in my implementation.)

I dislike automatically adjusting difficulty levels; manual control of difficulty levels is much better.

Skippable cutscenes is a very good idea; I agree. The ability to pause and rewind cutscenes can also help. However, my own preference is to just not have any cutscenes.

Fast forward function and pause function for game play is good.

Free look is good for puzzle games that you cannot fit the entire puzzle on the screen at once. (Sometimes the entire puzzle will fit on the screen at once; you do not need a free look function since you can already see everything.)

They mention people who cannot read English. Sometimes the writer might not know the other language, but can accept contributions of translations of documentation in other languages. (I will accept that, but currently don't have any.)