I add to attachment updated file lang-sla.tex (some heads had wrong translation) and sort-lan files (mkii and lua), which now sort czech index as a norm says. There is just minor problem with MkIV version. Normally in czech accented characters are sorted as non accented, only when all characters are same (eg. "byt" and "být") accented chars. are put after non accented ones. In MkII this is completely fine, but MkIV sorts both ways (sometimes it sorts correct, sometimes not) Just for case I put in the archive file I use to test czech sorting. Problem I describe here, can be seen on words under letter L.

And just one last question. I was playing with translation of user interface (for my bachelor thesis) and I wasn't able to add a new one. I tried to put some test translation in mult-def.lua and even modified mtx-interface.lua. I was able to generate messages file (mult-m**.tex) for my experiment, but i can't figure out how to generete mult-**.tex as well.