I wish.. I'm not sure, I have a book here, and I don't know. Having the context in mind, it is possible.But, if you two are native speakers and if you have never heard of this, I guess it has to be a typo. Thanks, that's a relief! I was wondering how to translate this.
If you want another native speaker's oppinion, I agree - it has to be a typo. "Speak the truth" is a pretty common expression. "tn" is not even a combination of consonants that can be pronounced in English. (Okay, maybe I'll be deluged with examples of perfectly common "tn" words - but I sure can't think of any, except maybe for compound words where the "t" and the "n" would belong to different