I have never heard anyone in England say "The lightnings...". I have often heard "The lightning bolts..." or "The lightning strikes..." or simply "The lightning is very powerful".
Thanks for the insight! I knew I could also learn some English even if the lesson is supposed to be on Romanian! Is it the same for thunder?
I am no expert, but I don't think that you can use 'thunders' as a noun. We use 'thunderclap' to describe the sound of thunder and for the plural: 'thunderclaps'. 'Thunders' is used as a verb. For example: "The God of glory thundereth (thunders)" în Psalm 29v3.
As RobBeckett said, "The lightnings are very powerful!" is not English. The plural form "lightnings" does not appear in any standard form of English. It should be translated, "The lightning bolts are very powerful!" or the Romanian plural should be rendered by an English singular, "The lightning is very powerful!"
A real problem of translation here. May I suggest "the lightning flashes are very bright"? As others have said, lightning does not have a plural in English.
Maybe they are referring to the Lightning fighter jet od the 60s. The Ligntnings were powerful.