When you ask a question using the inversion the verb has a subject, "inversion" means here inverting the verb with its subject.
- Parles-tu français ? The subject is tu.
When you give an order (imperative) the verb does not have a subject (and there is no inversion whatsoever).
- Parle français ! There is no subject, just the verb (and an object here).
That was a basic case. Now I'm going to use the reflexive verb se laver and it is a little more complicated.
Question with inversion: Te laves-tu les mains ? The subject tu is after the verb, like in the previous example. In front of the verb we have the reflexive pronoun.
Imperative: Lave-toi les mains. There is still no subject, neither before nor after the verb. Toi is not the subject, it is the reflexive pronoun.
Parles-toi Français is wrong, it just can't exist.
In order not to be confused I suggest you learn how to conjugate a reflexive verb. In the following sentences the reflexive pronoun is bolded. The verb is se laver.
Je me lave
Tu te laves
Elle/il se lave
Nous nous lavons
Vous vous lavez
Elles/ils se lavent
Question with inversion :
Me lavé-je ?1
Te laves-tu ?
Se lave-t-elle/il ?
Nous lavons-nous ?
Vous lavez-vous ?
Se lavent-ils ?
Notice that in the imperative the reflexive pronoun te becomes toi (toi is called an emphatic pronoun but it is not important you remember what it's called at that stage, you'll have other occasions to use it and lean more about it). What I'd suggest you do at that stage is to make sure you know the subject personal pronouns, you can conjugate a reflexive verb and know how to use the reflexive pronouns and don't confuse the lists since some pronouns are common to both lists, but not all.
For further study :
Reflexive verbs on Collins grammar, on Learn to French
1 An accent is added on the "e" (lavé) to facilitate the pronunciation. But with je the est-ce que question (est-ce que je me lave ?) is more usual.