NOTE: Please do not include "(en-US)" in the title of English articles. See Wiki Governance: Whether or Not "(en-US)" Should be Added to the Title of English Articles.
Also, you need to include the code as a tag at the bottom of the article. For example, the tag for an Italian article in the English language Wiki would be "it-IT". This is so that we can click the tag and see all the articles in that language (click the links below to see). Because readers can filter by multiple tags, this allows them to see only the articles in a tag list that are in a specific language and on a specific topic. Not only is this practice convenient for the people who read that language, but it is also necessary for when we migrate the articles to a language-specific Wiki version.
Some of the codes below are linked to the tag pages that list out all the articles that use that tag (in other words, click the language code to see all the articles in that language):
Primary localization languages
Other languages