A freelance translator usually works alone and will translate and then proofread a document. A translation agency will usually have different people translate and proofread, thereby providing a double proofreading. Agencies also offer management services for multi-language translation projects. Translators do not usually provide multi-language management because translators are only fluent in specific languages. Agencies often have more technological capabilities and can offer desktop publishing, and screen capture services.
Translators usually translate into their native languages only.
No matter how experienced or educated a translator is in a foreign language, it is still a foreign language. People are generally more comfortable writing and reading in their native languages. When working in your mother tongue, you instinctively have knowledge that is not easily learned. Grammatically and culturally it is best to work with native speakers of a language. A person will express themselves better in their native language.