Eniştem geç kalınca biz çayı içtik, o gelince ayran içmeyi tercih etti.

Eniştem means my brother-in-law.

• enişte = brother-in-law
• -m = my

So Turkish often shows possession by adding a suffix directly to the noun, instead of using a separate word like my.

A small cultural note: Turkish family words can be more specific than English ones, but brother-in-law is the usual translation here.

Geç kalmak is a fixed expression meaning to be late.

Even though kalmak by itself often means to stay or to remain, in this expression geç kalmak works as a single idea: to arrive late / to be late.

The suffix is attached to kal- because that is the verb part of the expression, while geç is describing it.

So:

• geç kalmak = to be late
• geç kalınca = when/since he was late

This suffix often means when, once, upon, or sometimes since/because depending on context.

It turns a verb into a time-related or cause-related clause.

Examples from the sentence:

• geç kalınca = when he was late or since he was late
• gelince = when he came

So Turkish is linking events without needing a separate word like when at the start of the clause.

Because of vowel harmony.

The suffix changes shape to match the last vowel of the verb stem:

• after a / ı → -ınca
• after e / i → -ince
• after o / u → -unca
• after ö / ü → -ünce

So:

• kal- has a, so → kalınca
• gel- has e, so → gelince

This is a very normal Turkish pattern.

By itself, gelince does not strongly fix the tense in the way English does. The time reference is understood from the rest of the sentence and the context.

In this sentence, the main verbs are in the past:

• içtik = we drank
• tercih etti = he preferred

So gelince is naturally understood as when he came.

In another context, it could mean when he comes:

• O gelince haber ver. = Let me know when he comes.

So the form is the same, but the overall sentence tells you the time.

That is true: Turkish often omits subject pronouns because the verb ending already shows the subject.

For example:

• içtik already means we drank
• tercih etti already means he/she preferred

Here, biz and o are probably used for clarity and contrast:

• we drank the tea
• he preferred ayran

They help highlight the change of subject. Without them, the sentence could still work, but it would sound slightly less explicit.

This is about the direct object and specificity.

çayı

The ending -ı is the definite accusative. It usually means the object is specific or known.

• çayı içtik = we drank the tea / the specific tea

ayran

Here ayran has no accusative ending, so it is more general or indefinite inside the phrase ayran içmeyi.

• ayran içmeyi tercih etti = he preferred drinking ayran

So the contrast is:

• çayı = a specific tea
• ayran = ayran in general, as the type of drink he chose

Also notice that içmeyi does have an ending, because the whole action drinking ayran is the object of tercih etti.

Because after tercih etmek, if the thing being preferred is an action, Turkish normally uses a verbal noun in -ma / -me, often with the accusative ending.

So:

• içmek = to drink
• içme = drinking
• içmeyi = the drinking / to drink, as an object

Therefore:

• ayran içmeyi tercih etti = he preferred to drink ayran

İçmek tercih etti is not the normal structure here.

This pattern is very common:

• gitmeyi tercih etti = he preferred to go
• beklemeyi tercih etti = he preferred to wait

Because tercih etmek is a compound verb.

• tercih = preference / choice
• etmek = to do, used as an auxiliary in many compound verbs

Together:

• tercih etmek = to prefer

In the sentence, it is in the past tense:

• tercih etti = he preferred

Turkish has many verbs like this:

• yardım etmek = to help
• kontrol etmek = to check
• fark etmek = to notice

So this is a very common verb-building pattern.

Both are in the simple past / definite past with -di.

içtik

• iç- = drink
• -ti- = past
• -k = we

So içtik = we drank

tercih etti

• etti is the past form of etmek
• third person singular often has no extra personal ending

So tercih etti = he/she preferred

This tense is used for completed actions, especially when the speaker presents them as known facts.

Yes, very often it can.

The -ınca / -ince form can express:

• time: when
• cause: since / because

In this sentence, both ideas fit naturally:

• When my brother-in-law was late, we drank the tea
• Because my brother-in-law was late, we drank the tea

Usually the context tells you which nuance is stronger. Here there is a slight cause-and-result feeling: his being late explains why we drank the tea first.

The word order is fairly natural and standard, but Turkish does allow some flexibility.

The basic structure here is:

• subordinate clause first: Eniştem geç kalınca
• main clause: biz çayı içtik
• new subordinate clause: o gelince
• final main clause: ayran içmeyi tercih etti

This is a very normal Turkish way to present the sequence.

You can move things around for emphasis, but that changes the focus:

• Çayı biz içtik emphasizes we
• Ayran içmeyi o tercih etti emphasizes he

Even with flexible order, Turkish usually likes the main verb near the end of its clause, so the original sentence sounds very natural.