Then "accessiblity" in general is not niche, it effects everyone or almost everyone.
But "accessibilty" is a broad concept, applying to all sorts of different unrelated needs. Vision impairment, cognitive differences, mobility needs, etc.
Some of them effect more people than others. Some of them will be "niche", effecting few people. it is just a fact, right? It is faulty logic to say that because "accessibility" effects everyone, every single accessibility accomodation is also therefore of use to everyone. It's not so.
How much need is there for multi-lingual screen-reading? I have no idea. It's obviously not universal -- I don't need it for instance, although I may need other kinds of accessibility attention -- but there may be lots of need for it! But we can't prove it one way or another just from language games around the general concept of "accessiblity".
Whether developers ought to accomodate even niche accessibility needs is a separate ethical or practical argument.