Use search terms from the language of interest. (Special characters may or may not be detected in your search, so try the search with and without them. (Example: “El Niño” OR “El Nino”)
Search in English, but limit your results to a particular language. Novanet, and many library databases have search facets that allow you to filter your results by language. In Novanet and EBSCO databases, you can find these facets on the left side of the page; you may have to search around for them in other databases.
Many databases search only within the titles and English-translated abstracts of articles, rather than in the full text. So you may need to use key English terms in your search.