Since I spend an inordinate amount of time studying 5 languages, and since I also have an unhealthy interest in language eedagogy and language-courses, as well as a rabid interest in language acquisition more than grammatical-linguistic knowledge about languages, I am working on a rather crazy piece of lexicography.
I have a spreadsheet set up, in which I place items of vocabulary from time to time, and then attempt to fill in the other columns for other languages. Naturally, languages not having 1-1 mapping, this is a little messy. Nonetheless, it's very enlightening. I hope that eventually I will have a rather comprehensive database, and might make it available for people (whoever they are) who might find it useful. It's also rather nice, in that I come across rather conversational/contemporary words in some languages, and then have to go looking for corresponding words/phrases in ancient languages.
At the moment the lexicon has English, Ancient Greek, Latin, German, and Scottish Gaelic. At some point I may add some Biblical Hebrew.
I also have a sub-lexicon specifically for noting in-language terminology for Grammar.