When I went to school I was taught that 16 oz was a pint and two pints equaled a quart. I was also taught that a liter was a little larger (1.8 oz) than a quart. Thus I conclude that a half liter is 500 ml rather than 250 ml as described in this article.
When I went to school in the 1980s Asia the old traditional units were long banished from schools and they were busy burying the imperial units as well. You got through the school and wouldn't realize what a pound or an inch means. All you got into drill was litre is the basic unit for measuring measure and 1 L = 1000 mL.
And in fact I only got to know what a pound is later in life when I read conversion table 1 kg = 2.2. pounds, or approx 1 pound ~ 450 kg.