This tip is about enabling the use of all characters in a Hungarian keymap, but the idea may be useful for other languages as well, hence the title.
There are four different Hungarian keymaps, depending on the infamous y-z key swap and the number of keys on the keyboard (101 or 102). For 101-key keyboards there is no separate 0 (zero) key, it is accessible by Alt-i'. The Happy Hacking Keyboard has a layout similar to 101 keys, so this must be used there as well.
Important punctuation characters are accessible with mappings using the Alt key, so we have to disable menu-shortcuts using the Alt key with the following setting.
:set winaltkeys=no
If this setting is enabled, we can define the missing keys. Here are the most important ones:
" Combinations accessible with the Alt key
<M-`> 0
<M-q> \
<M-w> |
<M-f> [
<M-g> ]
<M-x> #
<M-c> &
<M-v> @
<M-b> {
<M-n> }
<M-m> <
<M-.> >
<M-,> ;
These lines can be appended to your $VIM/vimfiles/keymap/magyar_utf-8.keymap file.