Freeciv

The ambiguous words are:

Reduces the unhappiness caused by aggressively deployed military units owned by the city by 1 -- in other words, it neutralizes the unhappiness caused by a single military unit (except under Democracy, where a single unit makes two citizens unhappy). Each city also avoids one shield of upkeep for units.

Compare this to the totally unambiguous wording for Shakespeare's Theatre:

Gives 1 additional luxury to every city, and 6 luxuries to the city where it is located.

With the Statue of Zeus either:
a) every city gets +1 content
or
b) the city that built it gets +1 content

If the answer is b), then definitely drop the word 'also' which is the root of the confusion. Also, for good measure, say something like "the city that built it".

If the answer is a), then add in the word 'every' or 'each' somewhere appropriate.