Technically speaking, these are already possible, they only require that you program them for your project to suit your needs. So, how's your Chinese? As it is the Chinese elder programmers that would potentially fulfill such a request, and just like the Nextion, their needs are of course met first. (It is why version 0.38 has been out for almost a week and we only have 0.37). And which language is this keyboard suppose to be in? There are several iso-8859 character sets for everything to be translated to. And what % of the screen is this keyboard suppose to consume? I think many would prefer so many variations that there is not a standard to be had. And finally, why chew up any of the remaining space for firmware for something that is not included in every project?
I think I'll recommend that if you want it, you find a way to program it without chewing up firmware, and you contribute it back to the group as I have done with for the Fonts with the ZI Editor. Perhaps with some more thought surrounding your requests you might consider exactly what kind of workload you are asking of someone else to engage in that should have been your responsibility.
Perhaps I could also make a request for a StoryBoard-to-CompiledTFT feature where many other programmers can merely do all the work for me.
Perhaps while waiting for whether or not this functionality is to be integrated into the Nextion Editor, maybe you might consider some of the Keyboard solutions in the Nextion Gallery Example Keyboard that other users have graciously provided to the group. Most recently Hugo Arganda has put a good effort into this with his keyboard.
I am now reviewing all of the Feature Requests, this will take some time, patience please.
Text Input - carried forward