It is displayed at the shopping cart block and summary.
I can deactivate/activate to print this in the corresponding Views (Footer: "Commerce Line Item: Line item summary" → "Item quantity").
It prints as "1 item", "2 items", "3 items" and so on.
I'm not sure which string is the right one. To test it I translated all strings that look like the right one, but none of them worked. It always prints as "item"/"items" for all languages.
Needs work
1.0
Internationalization
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Same applies to the summary block. Currently it relies on "item" or "items" translated elsewhere. But in order for it to be specifically translatable, line 173 of commerce/modules/cart/src/Plugin/Block/CartBlock.php should read
'#count_text' => $this->formatPlural($count, t('@count item'), t('@count items')),