Learn Farsi: متخصص‌ها بر تلفات رعد و برق تاکید کردند. - The specialists stressed the casualties of the thunderstorm.

In Farsi, the compound verb تاکید کردن (ta'kid kardan, to emphasize or stress) doesn't take a direct object. It translates literally as "to place emphasis on something". You will usually see it paired with the preposition بر (bar, on) or روی (ru-ye, on).

رعد و برق (ra'd o barq) translates as "thunderstorm", but what is the literal meaning?

It literally means "thunder and lightning" (رعد, ra'd = thunder; برق, barq = lightning/electricity). In Farsi, this compound is the standard way to refer to a thunderstorm, rather than using a general word like طوفان (tufân, storm).

Is تلفات (talafât) a plural noun, and does it only mean "casualties" in a medical or military sense?

Yes, تلفات is an Arabic-style plural meaning "losses" or "waste". While it is the standard word for human casualties or fatalities in disasters like this thunderstorm, it can also refer to broader material damages depending on the context.

If I wanted to apply this lesson's topic and say "Even the specialists stressed...", how would I add حتی (hattâ) and هم (ham) to this sentence?

You would place حتی immediately before the focused noun phrase, and هم right after it. The sentence would become: حتی متخصص‌ها هم بر تلفات رعد و برق تاکید کردند. (Hattâ motekhasses-hâ ham...).