The item by title search page has two entry fields that are designed for searching for items that already have a page on a Wikimedia site and may be in the Wikidata system. The left field, which says "Site:" is where you put the language of the Wikimedia site page that corresponds to the item you want to add. Most Wikimedia sites have equivalent editions for different languages which are represented by a code. For example, the code for English language is en and the code for French language is fr. This code can be found in the URL; so en.wiktionary.org is the English Wiktionary and en.wikipedia.org is the English Wikipedia, while fr.wiktionary.org is the French Wiktionary and fr.wikipedia.org is the French Wikipedia. A screenshot that shows where to locate a language code for a Wikimedia site is available here.