From Joomla! Documentation
Categorisation is an important part of grouping like pages together. It can be used as an alternative to finding content when pages are not properly linked to each other.
One thing to be aware of is that when translating a page, any 'category' links in the page should be modified to also include the appropriate language code. They should also not be confused with an actual link.
Category links appear to look just like a standard wiki link.
[[Article]] as compared to [[Category:Article]]
The difference is the word and colon symbol, Category: in front. Category: is a special term used to place the page in a category. Above, Article is a link, Category:Article, places the page in the category Article.
The translation of a category is very easy, just add /<language code> to the end of the category name. Here are a few examples.
[[Category:Article/fr]] for the French version [[Category:Article/nl]] for the Dutch version
There are some more methods to learn, so read on.
For example, if you translate a page from English to Spanish (language code es) and the page contains the following category:
You need to add /es to the end of the category name.
Category pages can be translated as well (which should be quick - most are blank except for containing a parent category) and will be part of a special categorisation project when ready. If you translated the category properly, you should see it at the bottom of a translated page as a colored box with white lettering. Red means the category does not exist yet, please don't worry about this. See the first sentence of this paragraph.
What are sort keys? Sort keys are the method Mediawiki uses to sort pages alphabetically on a category page. They are added after a pipe
| symbol. If you want, you can override the title of a page. For example, you have a category called
[[Category:Help]] on the page Getting Help. When a person views the "Help Category" page, they will see the page Getting Help under the letter G. If an editor uses a sort key,
[[Category:Help|A]] for their category link, Getting Help would be under the letter A. The code
|A tells the "Category Help" page to show the page under the letter A instead of G.
All translations have an English source page/<language code> URL. Since the source page is in English, the sort key would automatically become the page's name if it is not set. Getting Help would be under the letter G on the "Category Help" page. In normal translations, setting a sort key is usually not necessary. Currently, there is only one category which setting a sort key is recommended, the category Glossary definitions. This is because an alphabetical list is created from the pages in this category by its sort key.
Why? and Why not? In some languages, a translated word or the page name might not start with the same letter in English. For example, Access Control List is translated in Spanish as, Listado de Control de acceso. The link to the page "Access Control List/es" on the category page would be shown under the A because the true page name and the end of the URL is .../Access_Control_List/es. If you use:
[[Category:Glossary definitions/es|Listado de Control de acceso]]
This would set the sort key to, Listado de Control de acceso. Now, the Spanish version of "Access Control List/es" would be shown under the L on the category page. Using the sort key for a translation of a category may not be necessary. You will need to answer this question. Is the translated word(s) still be alphabetised in the same order as the translation language versus English?
[[Category:Glossary definitions/es|Componente]] on the page Component/es versus [[Category:Glossary definitions/es]] on the page Component/es
What You Should Not Do When Categorising
There are a few things you should not do.
Please do not do this:
Translate the word 'Category' and the name of the category.
[[Category:Development]] to [[Categorie:Ontwikkeling]]
Do this instead:
Translate just the name of the category.
[[Category:Development]] to [[Category:Ontwikkeling]]
Neither do this:
Use Special:MyLanguage/ or S:MyLanguage/, it is for links only.
[[Category:Development]] to [[S:MyLanguage/Category:Development/nl]]