Thomas

I think we are missing a point here.

"Andate" (stress on the "da") is the imperative of the "vos" form.
"Andale" (stress on the "an") is the imperative of the "tú" form, with "le" a regionalism I don't recall hearing outside Mexico.
(Sorry, but I can't type a capital "A" that is stressed.)

Sentate aquí = (Vos) Sit here.
Siéntate aquí = (Tú) Sit here.
Siéntese aquí = (Usted) Sit here.
Siéntense aquí = (Ustedes) Sit here.

Decime la verdad. = (Vos) Tell me the truth.
Dime la verdad.= (Tú) Tell me the truth.
Dígame la verdad. = (Usted) Tell me the truth.
Díganme la verdad. = (Ustedes) Tell me the truth.

We associate "vos" with Argentina, but it's heard in many Latin American countries. It certainly appears to be dying out in Costa Rica. Back in the 1970s, the joke was that only tourists and another group I won't identify for fear of offending others said "tú" rather than "vos", but today "tú" in the Central Valley clearly is more widely used than "vos".