There should be an article at the front. In any case, it's not wrong to have it there in English! Also, it's possible to say "are striking."
I see all these suggestions as acceptable, and it says the last modification was a year ago... Well, in any case, if it wasn't there, somebody added it :)
One of the two examples on the excercise page was "Teachers strike." That strikes me as not very ok in English. Typical of non-native lack of understanding of when the present continuous should be used. It's like a series "Drivers drive, teachers strike, doctors smoke cigars" lol
Out of context it sounds strange, but Учителі страйкують can indeed mean "Teachers strike". Like, yeah, that's what they do often, usually. Like, someone is discussing a related topic and you say "What can you do? Teachers strike".
As long as it's not the default translation, everything is fine. It should be accepted because it's correct in all ways. If someone read Учителі страйкують and somehow got a feeling of a general statement there, they have all the right to input it :D But it shouldn't be default because it's highly contextual.
Removed "Teachers strike" from the defaults. Added "Teachers are on a strike" instead.