Don't live or die with Altavista
While it is different from a electronic (pocket) translator in that it will do sentences, there is a wide gap between the output from the site and even mediocre Spanish. The more complex the sentence including just a lot of words, the odder the output.
The engine, Systran is available offline though and other than a bit of work to install it translates similarly and for some it is really better than nothing but you will not get very realistic translation but sort of functional.
I used it years ago on a laptop and even with the other person reading it they really got quite lost.