The problem:

In a multilingual environment "List All Categories" returns a possibly wrong articles count

Testing environment:

For other reasons I prepared a multilingual set-up that can be used to test this. It is a simple but exhaustive set-up:

• Set up a multilingual environment for 2 languages (e.g: en-GB and it-IT)
• Create 3 top-level content categories: one assigned to each language (counting "All" as a language)
• Create 3 articles in each category: one assigned to each language (counting "All" as a language)
• In both languages menu hierarchies create a menu entry for "Articles » List All Categories" (associated to the corresponding language)

Test:

In front-end visit the menu items for "List All Categories": you will see something like this:

As you can see all articles in each category are accounted for.
Now visit (click on) one of the three categories.
Only 2 articles will be displayed: the one associated to the current language and the one associated to "All" languages.
Thus, the count of articles in "Articles » List All Categories" is wrong (it doesn't "filter out" the unwanted language)

The cause:

The issue is due to the model for "List categories" using JCategories::get() which doesn't have provision for filtering items based on language

Possible cures:

• Reinvent the wheel and don't use JCategories::get() but a new similar method capable of filtering on language. (personally I don't like that...)
• Introduce in JCategories::get() a mechanism for filtering on language. This can be done either by 1) the introduction of an option (e.g.: 'filterlang') that filters results based on the current language and the "All" language, or 2) the introduction of a new optional parameter as an array of languages that JCategories::get() should take into account
• ... something else?

Fixing this will also have the beneficial side effect of possibly hiding categories containing only articles non-relevant for the current language (if "Empty Categories: Hide" is set).

What do you think?

N.B.: I'm personally unwilling to put my inexperienced hands on JCategories::get()'s queries and I'll need assistance for that, but I'm more then willing to help in any other possible way