WordReference translates acullá as "yonder." Is this a word that was only used in the past, or is it still used in modern Spanish today? If so, what regions does it appear in and how is it used?
As others have said, this is not a commonly spoken word, but is found mostly in poetry and writing, perhaps especially used in folk and children tales. I would use "acá y acullá" as the equivalent of "hither and yon".
As an aside, The RAE defines "acullá" as
- adv. l. A la parte opuesta de quien habla. U. en contraposición a adverbios demostrativos de cercanía, como aquí o acá, y menos frecuentemente a los de lejanía, como allí o allá, de los que puede ser un intensivo.
So "l(ocative?) adverb. To the opposite part of the speaker. Used opposite to adverbs that demonstrate closeness, such as "aquí" or "acá", and less frequently to those of farness, such as "allí" or "allá", of which it can be an intensifier.
I remember hearing
acullá from my grandmother long time ago. She was looking for her comb everywhere in the house. My mother asked her:
¿Qué pasa? (What's wrong?)
And my grandmother answered:
No puedo encontrar mi peine aquí, allá ni acullá! (I can't find my comb here, there and yonder[?]!)
So my best guess is that
más allá (over there maybe).
Spanish has six demonstrative adverbs. In order from nearest to farthest, they are aquí, acá, ahí, allí, allá, acullá. English has just three: here, there, yonder. That's why it translated it as yonder, as they are both the farthest from the speaker (incidentally, being from the [US] South, I use yonder in regular speech and so while allí sits on a grey area between my English there/yonder, allá and acullá would always be yonder for me).
Can't speak for other countries, but you will hear acullá ocasionally in the north of Spain (Asturias, especially).
It's a word only found in books and cartoons.
Oye ven, ¿Por dónde está la reina?
A veces por aquí y a veces por acá. Pero como yo soy gente importante siempre entro por acullá.