Translation:They do not speak themselves about fruit.
I believe "They themselves" is perfectly good English, and may be the most common way of using intensive pronouns in English. They are usually placed directly after the subject they intensify, or at the end of the sentence. So, the most natural ways I see of expressing this sentence are,
- "They themselves do not speak about fruit", or
- "They do not speak about fruit themselves".
"They do not themselves speak about fruit" sounds a little clumsy, but is understandable. However, placing the intensive pronoun between the verb and its objects, as in, "They do not speak themselves about fruit" is very problematic. Using this format could produce sentences such as, "I do not kick myself the football", and, "I do not play myself football", which are just wrong.
When placed after the verb, the reader may mistake the intensive pronoun for the (identical) reflexive pronoun, and think it is an object of the verb. Then, on finding another lone object following, they realise they have parsed the sentence incorrectly and have to re-parse it. When it directly follows the subject, ("They themselves ..."), or appears at the end of the sentence, ("They ... themselves."), it is much clearer that this is an intensive pronoun and not a reflexive one.