ミラさん が すんで いた うち を かいました。Who bought the house? Me or Mira-san?

Question

When I first tried to translate

ミラさん が すんで いた うち を かいました。

it was

1. Mira-san brought the house where Mira-san lived.

But someone said it would be

2. I bought the house where Mira-san lived.

I can see there isn't any mention of who bought the house. How do they know about whom they are talking about?

Answer 1

Did you notice that ミラーさん is marked with the subject marker (が) rather than the topic marker (は)? This means ミラーさん is the subject of the relative clause that modifies うち (I'm assuming you know the basics of relative clauses). And this usually also suggests that the subjects of かいました and すんでいた are different! If the subjects of the two verbs were the same, the sentence would have been written using は, with ミラーさん as the topic of the entire sentence, like this:

ミラーさんはすんでいたうちをかいました。

Mira-san purchased the house where he lived.

The structure of your sentence, however, suggests that ミラーさん is the subject of only すんでいた. The subject of かいました is not explicitly specified at all, but we can assume it's someone other than Mira-san.

ミラーさんがすんでいたうちをかいました。

[I/he/she/you/we] purchased the house where Mira-san lived.

EDIT: Note that が can still mark the subject of the entire sentence if the sentence is a special sentence called a 現象文. But this isn't a likely interpretation at least in this specific case.

Answer 2

We Japanese often omit the subject or object if it is clear from context.

Your first try: Mira San brought the house where Mira San lived

This may be correct if preceeding context is about Mira-san is living in rented accomodation. She might buy the house from previous owner for her sake.

1. I bought the house which Mira-san lived.
2. Mira-san bought the house which I lived.

These are also possible depending on context. I cannot judge which translation is correct only from this single sentence.

Stress　in pronunciation also affects the meaning.

Answer 3

For me, it feels like this:

ミラさん が すんで いた うち

(The place that Mira is living at)

を

(is)

かいました。

(bought (by someone))

So combine together, we don't know who is buying the property. All we know is that the property is where Mira is living.

Without further context, it should be "somebody bought the house that Mira lived". That "somebody" shall be depending on the context.