Translation:He said that it is an important event.
"..this is an important event." and "...this was an important event." are both accepted. Are both really correct? I think the first one is correct, but I'm not a native speaker.
The variant "said ... is" is closer to the Ukrainian sentences, even though it breaks the rule for the sequence of tenses. The variant "said ... was" just follows the rule and I would still accept it.
It is allowed to break the sequence of tenses "when the circumstance being expressed remains equally true now as it did when the speech act took place, and especially if the person reporting the words agrees that they are true or valid." This is what has been done in the Ukrainian sentence.