Seeing boxes instead of actually characters saddens me, I know, that these are rarely languages - some of them - but I like the support for every single one of them. I have done my searching, but I probably don't have the right words to search for, as I cannot find what I am exactly looking for. Sadly. If any of you have any help, I'd be glad. :>

Another thing, I wish to edit some of my keymap, mainly because I want the dead key ^ (which is obtain by ALT GR + ") + J makes this character: Ĵ. Which for those who do not know, is a character used in Esperanto. See this for more information.

If the world was perfect enough, I'd love to create every single character on my keyboard - which of course simply isn't possible. But I wish to know how to edit my keymap. So I might do more than I imagine as of now.

Thanks in advance.

Look to the xmodmap program to modify keyboard commands. Whether it will do what you want though, I don't know. You may need to use some kind of hotkey program to set it up as a key combination.

As for unicode, do you realize just how many characters "ALL" means? AFAIK, there are only a few fonts that have anywhere near that level of completeness. But I think there are some that have most of the significant character sets. You'll just have to search around for ones you can use.

Edit: I did a quick grep through the Debian package lists, and came up with this: keyboards-rg
I don't know if you'd be interested in it, but I thought I'd point it out.

And a few unicode fonts: