 | This is an essay. It contains the advice or opinions of one or more Wikipedia contributors. This page is not an encyclopedia article, nor is it one of Wikipedia's policies or guidelines, as it has not been thoroughly vetted by the community. Some essays represent widespread norms; others only represent minority viewpoints. |
 | This page in a nutshell: Non-English sources are allowed, but if you put in a bit more work, you can make them more useful. |
On the English-language wiki (hereafter, en), articles must be in English. Sources that you cite, however, can be in any language. In practice, most people who work on en are only fluent in English. If you use non-English sources, this makes it more difficult for those people to review your work. Here's a few things you can do to make life easier on everybody:
1. Find English sources. They may not exist, or may not be the best ones. If so, it's fine to use foreign-language sources. But, if you can find good English sources, it'll make it easier to review. They'll also be more valuable to most en readers.
2. Consider writing your article on another language wiki. If most of your sources are in, say, French, that's a hint that your subject might be mostly of interest to French readers, and you would do better to write your article on fr.wikipedia.org. Even if you decide to write it on en, you'll almost certainly want to translate it to fr (and link the two via a wikidata entry).
3. Provide a translation of the title and most relevant passages in your sources. Many of the citation templates (for example, Template:Cite_web), provide a trans-title field. You can also use the quote field to include directly in your citation a bit of quoted text, along with an English translation. See WP:FAIRUSE for guidance on how much quoted text is appropriate, vis-a-vis copyright restrictions.
4. If you find a source that you want to use, in a language you can't read, Wikipedia:Translators available can locate people to help with translations. While machine translations may be useful in helping you to understand a source, they're almost never good enough to use for quotes, or for making subtle inferences. Find a native speaker to help.
5. There are wikiprojects devoted to many countries. Asking for help on the project talk page (for example, WT:WikiProject France), is one way to find people who can help with translations and/or reviews.