Shopping cart plurals don't translate correctly into Russian

This is a Commerce issue. And we definitely can't fix it with a regular expression ;)

The recommended way to use format_plural is format_plural($quantity, '1 item', '@count items', array(), array('context' => 'product count on a Commerce order')), which should work in your case (can you check?)

And that's exactly what Commerce is doing for quantity, but not quantity_label, not sure why. Perhaps Ryan will have more insight.

The function is being used here as specified, it's just separating out the quantity from the label for the purposes of theming (i.e. having a wrapper around the number separate from the label). We definitely don't want a regex in the code, but I also don't think I understand why this isn't working for you or why this isn't but any other format_plural() does. Can you provide more info?

but this code knows nothing to do with 3 forms of plurals in Russian

Вы пишете про 5 items вместо 5 товаров, например? Просто недопереведено нашими коллегами. Зайдите в

/admin/config/regional/translate/translate

в фильтр вбейте "@count items" и переведите как "@count товара".

Затем ищем следующую форму: "@count[2] items". Переводим её: "@count[2] товаров".

Ну и конечно следим, чтобы правки делались в контексте product count on a Commerce order. И всё, всё будет работать как положено.

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Sorry for the answer in Russian, it concerns only the problem of our localization :)

The thing is that when you have cart block displayed, summary with total quantity should have 3 different forms, but in case of 'quantity_label' programmatically configured to have only 2: 'item', 'items' - there is no chance. With translation we could only have 2 plural forms in Russian: translation of 'item, and 'items', but it's necessary to have 3. Please, correct me if I'm wrong or misunderstand something.

With translation we could only have 2 plural forms in Russian

No, in our Russian language is 3 plural forms in this case. For example:

1 товар
2 товара
5 товаров

Same issue, If I understand it correctly, the numbering go like this:
1 товар,
2-4 товара,
5 -20 товаров

After 21 they start from 1 again but this time in cycles of 10:
21 товар,
22-24 товара,
25-30 товаров

31 товар etc
32-34 товара,
35-40 товаров

made correction to #6 changed "2-3" to "2-4"

Can Drupal do this? Use multiple plural forms?