"It is yesterday's bread."
Translation:È il pane di ieri.
Barra said that it's like an irregular case, not that it is one. However, it's really an exception to the general rule that final vowels are elided before words beginning with the same vowel, at least. Italian nouns (unlike those in Latin) don't have cases anyway, apart from the singular and plural forms.
It's important to stop thinking in terms of "word X in this language can mean word Y in that language" and start thinking in terms of "they say it that way in that language and we say it this way in this language".
Once you move away from concrete nouns like "apple", fewer and fewer words have one-to-one correspondences between languages, and this is especially true for prepositions. And even when the literal meanings roughly coincide, the usage will vary tremendously because different languages use different fundamental idioms. Why are we "in bed" but "on a train" in English? Why "in the morning" but "at night"? Just because we say it one way doesn't mean other languages should.
But regarding di vs da, the official translation says "It is yesterday's bread". Arguments aside that we don't really say it that way in English, it's a good reflection of how they say it in Italian. "the Y di X" is how they say "X's Y".
In English, we're only taught about the possessive, but that's only one aspect of what's called the genitive. We have it in constructions like "the head of the class".
So "di" corresponds more closely to "of" than "from" when you analyze its overall usage within the context of Italian. It's just that sometimes we phrase or frame things differently in English, saying that the bread is "from yesterday" rather than "of yesterday".
È il pane di ieri is to
Il pane è di ieri as
It is yesterday's bread is to
The bread is from yesterday. One has "bread" by itself in the subject, the other has "bread" in the predicate as part of a larger noun phrase.
Aside from being different grammatical constructions, they're not perfectly synonymous.
È il pane di ieri is talking about some particular bread.
Il pane è di ieri is a general comment about bread that might not even be present.
No, no, Harold. I was just saying that the translation was supposed to follow the order of words displayed. I agree that the final meaning is the same, but the two sentences I wrote to you are not equal in itself, just as their parallel translations. If I say your last name before your first name you continue being who you are, but it is not the same thing and I think that you would always like to be called by your first name. Maybe I have made my point now man. Sorry, but this is all I can do to help you. Farewell!
Different languages, different grammar rules.
In English, we can indicate possession by saying
X's Y. In Italian, the possessive is often
the Y of X. It needs the article. We have a similar construction in English: the top of the charts, the head of the class. It needs the definite article in both languages when it's in that form.