Interlanguage links are links from a page in one
These two types of links are created and handled differently and are discussed in different sections below.
Pages on Wikipedia can have a list of equivalent pages in other languages. For example, the Irish Wikipedia has a page on Ireland titled "Éire", so the English Wikipedia article on Ireland will link to the Irish one, and vice versa. For most people this list is shown on the left of the page, but this can be changed by changing the skin the site uses. This list is maintained in two places, Wikidata and the text of the page itself.
Wikidata is a separate project to create a collaboratively edited knowledge base. Part of this project is to centralize the interlanguage links for all the Wikipedia projects. The Wikidata entry for a page contains (among other things) a list of links for that entry in different languages. This list of links is then used for the list shown on the page in Wikipedia.
At the bottom of the Wikidata language list, notated 'Languages', there is a link labelled 'Edit links'. Clicking on this will reveal a new page:
If you get an error message like "Site link ... is already used by item Q....", this means that there is already an item in Wikidata pointing to the article you are trying to link to. Wikidata does not allow more than one item to point to a single article in a Wikipedia. There are then two cases:
Unfortunately, there is no mechanism in Wikidata at present for linking articles that are related, but different in a scope – it is possible to do this with local links however.
This section needs expansion. You can help by adding to it. (February 2017)
There are many ways Wikipedia articles of another language can be found. These include translating the article's title and its synonyms to other languages and searching for them on the respective language-versions of Wikipedia or on Google, Googling for
articletitle site:wikipedia.org -site:en.wikipedia.org (for non-English Wikipedia articles), checking the other language versions of related or superordinate articles and checking the other language versions of the article's categories.
To edit an entry on Wikidata, click on the edit link next to the entry you wish to edit. A textbox will appear allowing you to edit the entry. Click on save when you are done.
You can remove a page from the list of Wikidata's links. To do so click edit, then click on the remove link.
Before Wikidata, interlanguage links had to be recorded in the text of the page itself. The problem with this approach was that each language had to maintain its own separate lists. So for example, if the name of a page on the English Wikipedia changed, then each language that linked to that page would have to separately notice this fact and then change their own links.
For most pages, these links are no longer needed and can be safely removed, but you should verify that the local list and the Wikidata lists match before doing so. There is an automated tool to help with that.
The local links do however still serve some purposes:
[[it:Saldatura#Saldatura a punti]].
The local interlanguage
where the language code is the two-letter code as per
[[ar:عوالق]] [[el:Πλαγκτόν]] [[fa:پلانکتون]] [[he:פלנקטון]] [[ja:プランクトン]] [[ko:플랑크톤]] [[ru:Планктон]] [[ta:மிதவைவாழி]] [[te:ప్లవకాలు]] [[th:แพลงก์ตอน]] [[zh:浮游生物界]]
NOTE: These links are treated specially, and don't show up in the body of the text, but in a special sidebar section "Languages" listed by language name. They can go anywhere in the article source as their placement does not alter the visual appearance of the links on the rendered page except for the order. However, the convention is to put them at the bottom of the page. Remember, you only need these type links if you are overriding the information from Wikidata, otherwise you should edit the links on the Wikidata entry.
Featured or good articles are represented via Wikidata.