How often do you eat fish?
is on Tatoeba. The grammar seems different to English. The English "how often" is asking "with what frequency", whereas the Chinese seems to use 多久……一次 to convey the meaning "what's the time period between instances of":
You [你] how long [多久] eat [吃] one time [一次] fish [鱼]?
Question: Is 你多久吃一次鱼? a natural way to ask: How often do you eat fish?
I asked ChatGPT and it gave me all sorts of similar sentences, e.g.:
ChatGPT has no qualms with the question 你多久吃一次鱼?