I'm not a native English speaker so I'm struggling to get this right.
I understand (and this question confirms) that compound adjectives such as
Spanish-speaking, etc, must have a hyphen. In particular, for us non-native speakers, it really helps to instantly, on-the-march disambiguate some sentences, to tell if, e.g., we are referring to a Spanish person that is speaking right now, or about any person who can speak Spanish.
However, I'm finding more and more cases were the hyphen is omitted in compound adjectives, such as this in Wikipedia.
The Cannone da 90/53 was an Italian designed cannon
I know that Wikipedia is hardly a writing style reference, but this is far from a rare case.
My question: is this a plain error or is the hyphen considered optional nowadays?