What is the difference between "completarse" and "estar terminado"?

Question

I was trying to create my own sentences in Spanish and using a machine translator to check what I came up with. When I checked:

The trading must be completed by 4 this afternoon.

I was given this translation:

El comercio debe completarse para las 4 de la tarde.

When I tried translating another similar sentence:

Everything must be completed by tomorrow night.

I got this instead:

Todo debe estar terminado para mañana por la noche.

I did a search of "What's the difference between 'completarse' and 'estar terminado'?" but it did not lead to much. I also checked the Diccionario de la Lengua Española (DLE). Much to my surprise, it told me that the word "completarse" does not exist. This piqued my curiosity, so I decided to try to find some real world examples of the use of "completarse." I found some in El País, no less. They follow:

La transacción podría completarse a finales de 2018
The transaction could be completed by the end of 2018

La adquisición podría completarse en cinco días, ...
The acquisition could be completed in five days, ...

...la transacción debía completarse a más tardar ...
... the transaction was to be completed no later than ...

While the DLE may not recognize "completarse" as a word, clearly, it does exist if this Google Ngram is any indicator:

I'm going to operate on the presumption that the word "completarse" exists. The question that still remains for me is this:

When do I use "completarse" and when do I use "estar terminado"?

Or are they completely interchangeable?

As I see it, on the one hand, we have a pronominal verb — completarse — and on the other, a copula formed with "estar" + adjective (terminado). Collocations and general usage aside, are there any general observations that have been/can be made about these two types of structures with respect to their meaning?

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¿Cuál es la diferencia entre "completarse" y "estar terminado"?

Intentaba crear mis propias frases en español y usaba un traductor automático para comprobar lo que se me ocurría. Cuando comprobé

The trading must be completed by 4 this afternoon.

Me dieron esta traducción:

El comercio debe completarse para las 4 de la tarde.

Cuando intenté traducir otra frase similar...

Everything must be completed by tomorrow night.

Tengo esto en su lugar:

Todo debe estar terminado para mañana por la noche.

Hice una búsqueda de "¿Cuál es la diferencia entre 'completarse' y 'estar terminado'?" pero no condujo a mucho. También revisé el Diccionario de la Lengua Española (DLE). Muy a mi sorpresa, me dijo que la palabra "completarse" no existe. Esto despertó mi curiosidad, así que decidí intentar encontrar algunos ejemplos reales del uso de "completarse". Encontré algunos en El País, nada menos. Siguen:

[Véanse arriba en la sección inglesa.]

Aunque el DLE puede no reconocer "completarse" como una palabra, claramente, existe si este Google Ngram es algún indicador:

[Véanse arriba en la sección inglesa.]

Voy a operar con la presunción de que la palabra "completarse" existe. La pregunta que aún me queda es esta:

¿Cuándo uso "completarse" y cuándo uso "estar terminado"?

¿O son completamente intercambiables?

Como lo veo, por un lado tenemos un verbo pronominal — completarse — y por el otro una cópula formada con "estar" + adjetivo (terminado). Colocaciones y uso general aparte, ¿hay alguna observación general que se ha hecho o se puede hacer sobre estos dos tipos de estructuras con respecto a su significado?

Answer 1

There are two different things happening here.

Completar vs terminar

The difference between completar and terminar is as subtle as the difference between complete and end/finish. In fact, DLE says about completar:

2. tr. Dar término o conclusión a una cosa o a un proceso.

and terminar is, of course, "poner término". So both are practically the same, and there are just some collocations that sound better with one than with the other. A "process" (such as a "transaction") that is successfully brought to an end is usually said to be "completado", whereas the sentence "el proceso ha terminado" is more general and means that the process finished, either because it came to its natural end or because it failed or was interrupted.

Completarse vs estar completado (or terminarse vs estar terminado)

The difference here is also very subtle. In a sentence like

La adquisición podría completarse en cinco días

completarse is an instance of pasiva refleja, and it is equivalent to "ser completada". So we are mostly dealing with a ser/estar difference. "Ser completado"/"completarse" is standard passive, and refers to the action of something being completed. On the other hand, "estar completado" is the verb "estar" plus the adjective "completado", so it refers to the result of something being completed. So if you say

• La transacción debe completarse mañana a las 16:00

it means that the transaction must be done exactly tomorrow at 16:00. However, if you say

• La transacción debe estar completada mañana a las 16:00

it means that the transaction must be finished by tomorrow at 16:00, i.e., that it must be done any time before that. This applies to some of your examples, such as

La transacción podría completarse a finales de 2018

which means that the transaction might become complete near the end of 2018, but it is not expected to be completed before.

Answer 2

Use "He acabado" or "He terminado". Preferentially, I would use, "He acabado".

Completarse means 'to be completed' and is in the passive voice. Example:

Este trabajo puede completarse en dos horas = This work can be completed in 2 hours.'By someone' is implied which is always the case in the passive voice.

Never use the verb 'estar' with 'terminado' because it does not mean 'finished' or 'done'. It is poor/incorrect Spanish grammatically. You can say, 'He terminado', however. 'He' being the present tense of 'haber' and as an auxiliary verb, forms the present perfect tense: to have done...