Resist the temptation to do it yourself

Speaking is not writing. Oral fluency does not guarantee smooth, stylish writing. Even if you regularly negotiate successfully in French, German or Spanish, and spend lots of time in the countries where those languages are spoken, 99 times out of 100 your written command of a foreign language will be immediately recognizable as “foreign.” This may or may not be important. It may not be important if (1) your main selling point is price (price-driven clients will put up with a lot if they manage to understand the basics) or (2) you want to emphasize a certain foreignness (think Ahnuld and Zsa Zsa).