Learn Hardcore Turkish: Yazar dosyayı yedeklemediğini itiraf etti; o yüzden dizini yeniden kurduk. - The author admitted that he hadn’t backed up the file; so we rebuilt the directory.

yedekle = to back up
-me- = negation (not)
-diğ- = nominalizer (-dik/-diğ- turns a verb into a noun-clause: “the fact that …”)
-i = 3rd person singular possessive agreement (ties the clause to its subject)
-(n)i = accusative case (because this entire clause is the object of “confessed”)

So dosyayı yedeklemediğini means “that (he/she) didn’t back up the file.”

Why is there a y in dosyayı?

It’s the buffer consonant. The noun dosya ends in a vowel, and the accusative suffix is -ı/-i/-u/-ü. When a vowel-final word takes a vowel-initial suffix, Turkish inserts y to prevent a vowel clash: dosya + ı → dosya-y-ı = dosyayı.

Why is dosyayı in the accusative here?

Because it is a specific, definite object inside the subordinate clause: “(he) didn’t back up the file.” In Turkish, definite direct objects take the accusative. Without accusative (just dosya), it would mean “didn’t back up a file” or be read as non-specific.

Does dizini mean “the directory” or “his/her directory”? Why not dizinini?

In this sentence, dizini is most naturally the definite accusative of dizin (“the directory”), functioning as the direct object of kurduk: “we rebuilt the directory.”
Ambiguity note: dizini can also be “his/her directory” (3rd person possessive, nominative). If you clearly wanted “his/her directory” as a definite object, you would mark both possession and accusative: dizinini (dizin + i [poss] + ni [acc]). Here, context favors the simple definite object reading (“the directory”).

How do we know who didn’t back up the file in yedeklemediğini?

In nominalized clauses with -dik/-diğ-, the possessive ending marks the subject of the embedded clause:

-diğimi = that I …
-diğini = that you (sg) … / that he/she …
-diğimiz = that we …
-diğiniz = that you (pl) …
-diklerini/-dıklarını = that they …

Here we have -diğini, which is ambiguous between “you” (sg) and “he/she.” Context resolves it: with Yazar … itiraf etti, it naturally means “the writer (he/she) didn’t back up.”

Could we say itiraf etti ki dosyayı yedeklemedi instead?

You can, but Turkish far prefers the nominalized clause (… yedeklemediğini itiraf etti). The ki construction is grammatical yet more bookish or calqued from languages like English; it’s used, but less idiomatic in everyday speech for this verb.

Why is there a semicolon before o yüzden? Can I use a period or a comma?

The semicolon links two closely related independent clauses.
A period is also fine: … itiraf etti. O yüzden …
A comma would be less standard here unless you restructure (e.g., with a conjunction). Using the semicolon or a full stop is the cleanest.

What does o yüzden do, and how does it compare to bu yüzden, bu nedenle, dolayısıyla?

They all mean “therefore/that’s why/so.”

o yüzden and bu yüzden are common and relatively informal; o often points back to something just mentioned.
bu nedenle, bu sebeple, dolayısıyla are a bit more formal. All are fine here.

Is the word order fixed? Could I move things around?

Turkish is flexible with word order, though default is SOV. Variants that remain natural:

Yazar, dosyayı yedeklemediğini itiraf etti. O yüzden dizini yeniden kurduk.
Yazar dosyayı yedeklemediğini itiraf etti; bu yüzden dizini yeniden kurduk.
Within the second clause, you can place yeniden before or after the object: Dizini yeniden kurduk / Yeniden dizini kurduk (first is more common).

Why is it itiraf etti and not something like itiraf yaptı?

Because the correct verb is the light-verb compound itiraf etmek (“to confess”). The past tense is itiraf etti (“confessed”). İtiraf yapmak is not idiomatic.

Could we use -miş past (e.g., itiraf etmiş) here? What would change?

Yes. İtiraf etmiş adds a sense of report/hearsay or distance: “apparently/it seems he confessed.” With itiraf etti, the speaker presents it as a plain, witnessed or asserted fact.

Why negative -me- in yedeklemediğini instead of another form like yedeklemediğini olduğunu?

Negation is built directly into the verb with -me-/-ma-. You don’t add an extra olmak here. The nominalizer -dik/-diğ- already turns the negative verb into a noun-clause: yedekle-me-diğ-i-ni = “that (he) didn’t back up.”

What does yeniden kurduk mean exactly? Could I use tekrar?

yeniden kurduk = “we rebuilt/reinstalled/re-established (it).” It emphasizes doing it anew, from scratch.
tekrar means “again” in the sense of repetition. Tekrar kurduk is possible, but yeniden is often preferred for reinstallation/reconstruction contexts.

Is dizin the usual word for “directory”? What about klasör?

dizin is commonly used in computing for “directory.”
klasör often maps to “folder.” In some contexts they overlap, but dizin is the more technical/UNIX-like term.

How do I pronounce the ğ in yedeklemediğini?

Turkish ğ (soft g) isn’t pronounced as a hard consonant; it lengthens or smooths the preceding vowel. In -diğini, the ğ just lengthens the i sound; don’t try to pronounce a hard “g.”