Hi! This sentence is a natural sounding sentence to me, but it doesn't mean the same as the other translations. The translated sentences in both English and German are something that happened one time in the past, but this sentence is asking generally when would a particular thing happen (past, present, or future).

Note that the English "When does that happen?" is only indirectly linked to the German. It's possible that the Toki Pona sentence could mean either "When does that happen?" or "When did that happen?" @carlosalberto, is that the case?

This sentence sounds natural to me. It feels like something someone would say when asking about something that happens regularly or as a result of something else. You could segue into this question from a past event, though that might imply that it's likely to happen again.

@Biderl
Would you be so kind as to answer @AlanF_US about his question above?

@carlosalberto
I translate from German into Toki Pona. If there are any problems, I try to solve them. I am not responsible for English. Sorry.
@AlanF_US
Wann passiert das? = tenpo seme la ni li kama?
Wann ist das passiert? = tenpo seme la ni li kama [lon tenpo pini]?

@AlanF_US
The tense in Toki Pona sentences depends on the context (or is specified directly in the sentence, for example, through the use of "la" constructions or "lon" ("tenpo pini la..." — past tense, "...lon tenpo kama" — future tense)).

Sentences such as "tenpo seme la ni li kama?" (time-question (when) [context split] this [subject-predicate split] come/happen/become/...) do not specify the time directly, so they can mean any time depending on the context.

Yes.

Thanks, everyone. This means that everything is fine. The multiple meanings of the Toki Pona sentence will continue to indirectly link sentences that have different tenses in French, German, English, and so on, but that's just the way it goes.