It sounds like the perfect solution, doesn't it? It costs $0.00, and surely someone who is bilingual is just as qualified as a professional translator to translate your [insert any number of things your company could need translated], right? Unfortunately, it doesn't really work that way.
Bilingualism ≠ Good Translator
® Best Seller. It's just not true. To be a good translator, it is absolutely imperative that said person be a good writer. If you can't eloquently convey thoughts on paper (or via your keyboard nowadays), you do not have what it takes to render a high-quality translation. Not a member of the grammar police? You need to be commissioner of the grammar police as a translator. If Suzanne sometimes confuses 'they're, there, and their', chances are likely that she will make a mistake that embarrasses your company in the translation you had her do for free.
Let's say Suzanne isn't commissioner of the grammar police, but she's at least a card-carrying captain. That's great, but is Suzanne an expert in French grammar rules too? Does Suzanne know that the French use more noun clauses than we do in English? Does Suzanne know how to maintain language register between the two languages? Does Suzanne know that the French like to start out sentences or paragraphs with an explanation and end with the main point (or topic sentence), whereas in English we often make our main point immediately, then spend the rest of the sentence or paragraph explaining1? Not knowing all of these mechanical and cultural differences could make your translation sound like an awkward and stilted....well, translation.
The goal when translating a [insert any number of things your company could need translated] is to take the message from the original, then shape, mold and craft that same message into another language in the most appropriate way possible. A good translation should never sound like a translation. Professional translators have been educated on all of the above-mentioned topics. We learned about modulations, transpositions and equivalents. We studied and practiced how to translate for years before getting paid to do it. We can spot a grammatical error from a mile away (and we know that "spotting something from a mile away" is an Americanism that can't be translated word-for-word in French or other languages).
The fact of the matter is that professional translation is worth the cost for any text that needs to be publication-quality. If your company had a legal issue, would you consult your employee John who took one criminal justice course in college, or would you consult a practicing lawyer who is a member of your region's bar association? I rest my case.
Siepmann, Dirk. "Academic Writing and Culture: An Overview of Differences between English, French and German" Erudit. 2006. Accessed December 11, 2015. https://www.erudit.org/revue/meta/2006/v51/n1/012998ar.pdf.