I also have exact same issue...
I can add to the issue, with some potentially helpful observations.
I first experienced this issue on my Toshiba laptop running widows 10 with Intel processor / 4GB RAM. I had two issues with this laptop.
The issue of 'Failing to load characters'. The number and quantity of characters not loaded was not consistent. Sometime only one character would load and occasionally four characters would load. There was no consistency on which characters or how many of the five loaded or did not. Clicking the reload button of the saved editable character did not reload the saved character, but I was able to edit the character, to recreate to the best of my memory, the character as I previously saved them. I bought a skin pack to make it easier to reload my characters. These purchased skins would also not load on startup of Minecraft, but at least I could edit the character appearance to the purchased skins...
The second problem I was having (which is related, bare with me) was that Minecraft would stop responding quite regularly when closing command block programming/editing window. I tried all the usual things, like Application Reset, Un-install Reinstall, I even made a clean install of windows 10. nothing worked. I figured my computer was just not powerful enough to handle Minecraft.
I wanted a new laptop anyway, so I bought a Lenovo IdeaPad L340 AMD/Radeon and added maximum RAM. I installed Minecraft on it and it worked like a dream for weeks and weeks. Then after a while I had a few crashes when using the /tp command, and a few crashes when exiting command block edits. Then the 'failed to load character' thing started and now consistently will not load characters, though the characters do reload when clicking the reload button, so its not quite as irritating as my last laptop.
I began to wonder what changed on my new laptop that might have contributed to the problem, and I think that I pinned it down to when I installed 'Minecraft Education Edition'. I have since uninstalled Education Edition and I have not had any command/command block crashes since then (touch wood). The uninstall process of Education edition was a bit hairy, as it never completed the uninstall, the progress bar never reached half way and so (ctrl alt del) to end the process, reboot my laptop. Education edition was gone. However I am still left with characters not loading....
Question is, what can the installation of Education Edition change in the existing Standard Bedrock edition that is not undone when you uninstall Education version?
I have a large block of command blocks which I structure blocked to test its portability in local game 'my world'. There are two layers of Chain/Conditional/Always Active blocks, which when loaded to a new coordinate position, have reverted to Chain/Unconditional/Always Active. It's going to be pretty tricky to replace the blocks in the middle of the cluster, might have to clone the two layers, but if I'm going to do that, I might as well clone the entire structure... Really annoying as I'd hoped to share this model (when it's completed) with a realm I play in... The first image is the original construction which works like a dream. You can see the two rows of chained/conditional blocks. The second image is after moved/copied with a structure block. the two middle rows of chained command blocks have reverted to 'unconditional'...
[media][media]For what it's worth, the jd-gui decompiler will let you read those .class files. They don't look particulary scary; someone with access to minecraft source should be able to figure out where the patches have been made, roughly what those were and get a solid lead on what needs to be done to fix keyboard input in minecraft.
I would imagine all of these strings are internally unicode, so system locale should not be an issue (though doing something intelligent w/r to CJK unification presents some interesting challenges)
Perhaps this is a font issue?
Not being able to type in your native language is actually a pretty big issue to have. Particularly if your language is big on homonyms...
The issue here is not 'How do I build an IME?' but 'How do I do IME-friendly input in Java/lwjgl?' Some m18n best practices documents should help shed some light on this. Evidently, at least two people have found a way to fix this for minecraft (nihongoMOD and MinecraftIM), so this is not an unsolvable problem.
There are other input issues that deserve attention (the old release of lwjgl packaged with minecraft has some IME related bugs affecting at least linux) but IME support in vanilla minecraft would be a very, very nice thing to have, as nobody should have to mod minecraft just to be able to communicate.
I concur that this issue does indeed affect windows 10 minecraft and that the GUI reader works but not the Chat reader...