There's also (besides Tate's sequel of 7 more languages), Dimitry Zinoviev's 7 Obscure Languahes in Seven Weeks. I liked it a lot, even if it hurt my feelings a bit to have my beloved Forth be one of the obscure languages (the others were APL, SNOBOL, Occam, Simula, Starset, and M4) -- I'm old and nerdy, but hadn't even heard of Occam and Starset.