"y que el idioma de las direcciones esté en español."

Question

Hi,I don't understand why "estar" is in subjuntivo instead of indicativo.

Accepted Answer

Hola Wenli
Good question! The first thing to consider is the main verb followed by que in the sentence:
"...ando comprobando que el idioma de las direcciones esté en español.
Comprobar is considered a "verb of perception" (like ver, escuchar, as well as asegurarse, cerciorarse, verificar, comprobar...)
You could use both the indicative or the subjunctive with verbs of perception, so you could say: "En este momento ando comprobando la batería y que el idioma de las direcciones esté/está en español."
If we use the indicative (que está...) the speaker is perceiving something and declaring it. 
If we use the subjunctive (que esté...) the speaker is adding an element of "intention/influence", therefore we have to assume that the speaker is intentionally, actively checking that the Spanish language is set. 
To see this difference with other sentences and verbs of perceptions here are a couple more made up examples:

Tiene que verificar que no hay ninguna fuga de gas. 
He has to verify that there is no gas leak.
(here he is verifying what is perceived and confirm it)
Tiene que verificar que no haya ninguna fuga de gas. 
(here he is verifying and checking, doing something about it)
He has to verify that there is no gas leak.
 
Vimos que todo estaba en orden.
We saw that everything was in order.
Vimos que todo estuviera en orden.
We saw that everything was in order. (intentionally checking)

I hope this clarified it for you.
Saludos
Inma