So, in my mother language, there’s a compound word szalmaláng [‘sɒlmɒlaːŋɡ] /lit. straw-flame/. This word is often used in fine literature as an allegory to a sudden burst of enthusiasm and zeal that lasts only for a short time and dies very soon. It is often used in a phraseme, "szalmaláng-lelkesedés" /lit. straw-flame enthusiasm/
As an example, a poet would say:
"Megégetett a szerelem szalmalángja"
/lit.: I was burned by the straw-flame of love./
and mean: I was hurt by a sudden love that ended quickly. Or
"Beszterce városában nem szalmaláng-lelkesedés van, amely hamar kialszik, és hideg hamuvá lesz, hanem izzó parázs évszázados forrósága éget."
/lit.: In the city of Beszterce, there is no straw-flame enthusiasm that swiftly fizzles out and turns to cold ashes, but the centuries-old heat of glowing embers burns./
and mean that in Beszterce, the enthusiasm of people doesn’t die out quickly; on the contrary, it has been consistently there for centuries.
What would be an English alternative for this word, szalmaláng? I’d prefer to have a similarly allegoric single literary word or a phraseme, but an idiom would also work.
As usual, there is no one phrase that will fit all uses, but many that might be applicable.
- flare-up is a very similar metaphor (both examples you gave engage in wordplay about fire), but its use is mostly limited to unrest and medical conditions.
- flash in the pan also uses a metaphor of combustion, but applies mainly to brief effort or interest
- As Greybeard suggests, nine days’ wonder could be applicable for something that was briefly of general interest or celebrity
- In many cases, a fairly literal translation might be the best route (including preserving the wordplay of the examples), like "brief [or feeble, spasmodic, short-lived, etc] flame"