Learn Croatian: Kakva užasna tragedija! - What a terrible tragedy!

In exclamations, you use kakav (and its forms like kakva or kakvo) when you are modifying a noun, similar to the English phrase "What a...". Since tragedija is a noun, we must use kakva. You would only use kako (How...) if you were exclaiming about an adjective or adverb on its own, like Kako užasno! (How terrible!).

Why does kakva end in -a in this sentence?

Kakav behaves like an adjective, so it has to match the gender, number, and case of the noun it modifies. Because tragedija is a feminine singular noun in the nominative case, both the exclamation word (kakva) and the adjective (užasna) must take the feminine nominative -a ending.

In English we say "What a terrible tragedy", so why isn't there a translation for "a" in the Croatian sentence?

Croatian doesn't have indefinite articles like "a" or "an". The exclamatory word kakva directly attaches to the noun phrase užasna tragedija without needing any extra words between them.