Learn Hardcore Turkish: Her ailede bir gelenek var.

Her means “each” or “every.” It’s used before a noun to indicate that you’re talking about all members of a group individually (in this case, every family).

What is the function of the suffix -de in ailede, and why is it -de and not -da?

The suffix -de is the locative case, meaning “in” or “at.” You attach it to aile (family) to get ailede (“in the family”). According to Turkish vowel harmony, because aile ends in a front vowel (e), you use -de rather than -da.

Why is there bir before gelenek, and why isn’t there a definite article like in English?

Turkish does not have “the,” and bir serves as the indefinite article “a” or “an.” So bir gelenek literally means “a tradition.” If you wanted to say “the tradition,” you’d simply say gelenek without bir, relying on context.

What does var translate to, and why is it used here?

Var indicates existence and corresponds to English “there is” or “there are.” In Her ailede bir gelenek var, it tells us that “a tradition exists in every family.”

Why is gelenek singular instead of plural?

Because the sentence states that each family has one tradition. If you wanted to express that every family has several traditions, you would pluralize it:
Her ailede birçok gelenek var or Her ailede gelenekler var.

Is it possible to change the word order, for example to Bir gelenek her ailede var?

Yes, Turkish word order is relatively flexible. Bir gelenek her ailede var is grammatically correct but slightly shifts emphasis onto gelenek (“A tradition exists in every family”). The original order (Her ailede bir gelenek var) is more neutral and common.

How would you form a question like “Is there a tradition in every family?” in Turkish?

You add the question particle -mı/-mi after var and adjust vowel harmony:
Her ailede bir gelenek var mı?
This literally means “In every family, is there a tradition?”