This is the 693rd most frequent Ukrainian word.
таку
The word "таку" in Ukrainian is a form of "такий" and means "such" or "this kind of" depending on context.
Here, "таку" is used as an attributive adjective in its feminine accusative form, referring to the bag, which is a feminine noun in accusative case.
Я хочу таку сумку.
I want such a bag.
In this sentence, "таку" modifies the feminine noun "дівчину" in its accusative form, indicating specification.
Ми бачили таку дівчину.
We saw such a girl.
"Таку" is used here in two contexts: first to describe a situation with the word "така", and second to specify the kind of mistake in accusative feminine form.