"The robots repair each other."
Lots of robots are incapable of using language. Not everything that can use language counts as a "being." Speaking computers don't count as beings capable of using language, for instance.
We know that even Klingons waffle with this when confronted with edge-cases, like talking parrots or androids. Think of some episodes of Star Trek: The Next Generation, where some people insist on calling Data an "it" instead of a "he." Sometimes you just don't know how to classify something linguistically.
The creators of this course have assumed that robots are not beings capable of using language. They should probably add in the tips and notes, if they haven't already, that for the purpose of this course they're assuming all robots are not beings capable of using language. They should consider issuing an apology to any language-using robots reading the page.
They should probably add in the tips and notes, if they haven't already, that for the purpose of this course they're assuming all robots are not beings capable of using language.
Good idea! I've added something to the tips and notes of the "Simple Sentences" unit (aka "Sent. 1"), which introduces the noun qoq and already has a section on the three plural markers.
The note should be available at https://www.duolingo.com/skill/kl/Simple-sentences/tips-and-notes in the "Plurals" section in a day or so at the latest.
And to be completely clear, it is not the prefix that specifies, nor the root verb itself, but rather the use of the -chuq suffix, which can only be used when the subject is plural. Also, even if it was not completely clear, there is no rule about leaving it off, even when it is not clear, and making your listener work harder for the meaning. However, even though we don't think about Klingon society being polite in the ways we expect, I like to think that in this respect, they have a touch of politeness.
Note that the argument is not about whether or not they use language, but whether they are beings that use language. They have to be both beings and language users to get -pu'. This is getting into "does it have a soul?" territory. (I almost misspelled that sole! HoSDo have no feet, yet are beings.)