Please read Koz’s reply. You can reverse your words, but someone else can reverse that to get your words back. You can use voice changing plugins (I don’t know good ones for Linux) but people who know you will still recognise your delivery and cadences.
If this is for a legal experiment, I recommend consulting your lawyer.
I’d advice running your text multiple times through Google Translator, then using a speech synthesizer.
Can’t guarantee you that it’ll work, but that shold seriously mess up the way you composed the text, probably partialy distorting it beyond intelligibility.