Do you perfectly know a foreign language? Then you can take advantage of your ability to translate texts, by taking a look at the sites that require experts in this field. If you intend to become a professional translator, remember that you will need to have a degree in Languages or a more specific one such as Interpreting and Translation.
There are many blogs, sites, and newspapers that need updated, original and always fresh content. If you have an aptitude for writing then you can send your application to the sites you would like to work for.