Learn Turkish: Kargo ulaştı mı? - Did the package arrive?

The root of the verb is ulaş- (to reach or arrive). Because it ends in ş, which is a voiceless consonant, the d in the past tense suffix changes to a t to make it easier to say. Then we add ı to match the last vowel, giving us ulaştı.

How do we know to use mı for the question particle here?

The question particle follows 4-way vowel harmony based on the word right before it. The last vowel in ulaştı is ı, so the particle must be mı. Remember that it is always written as a separate word, even though it follows vowel harmony rules as if it were a suffix!

Why is there no personal suffix at the end of ulaştı?

In the Turkish past tense, the 'he/she/it' form (3rd person singular) doesn't take any extra personal endings after the past tense suffix. Since the subject is kargo (the package), we just use the verb root plus the past tense suffix: ulaştı.

Could I say Kargo geldi mi? instead?

Yes, you absolutely can! Geldi means 'came', so Kargo geldi mi? means 'Did the package come?'. However, ulaşmak specifically means 'to reach a destination', which is the most natural verb to use in Turkish for mail and deliveries.