Learn Croatian: Jesu li izašli prekjučer? - Did they go out the day before yesterday?

To make a yes/no question, you need the long form of the helper verb. The regular statement for 'they went out' uses the short helper verb su. The long version of su is jesu, so the question must start with Jesu li.

Where is the word for 'did' in this sentence?

Croatian doesn't use a 'do' or 'did' word for questions. Instead, past tense questions use a helper verb (a form of 'to be', which is jesu here) plus the main action word (izašli). It works more like asking 'Are they gone out?'

Why does the action word izašli end in -i?

The -i ending tells us that 'they' refers to either a group of males or a mixed group of males and females. If we were asking about a group of only females, the word would change to izašle.

Is the word prekjučer related to jučer (yesterday)?

Yes! It combines the prefix prek- (meaning over or across) and jučer. So prekjučer literally translates to 'over yesterday', which makes sense for 'the day before yesterday'.