Being bilingual is not enough
Someone may speak two languages well enough to communicate with native speakers, but the skills demanded of translators go beyond effective communication.
It's not only words
Translators must bridge linguistic and cultural gaps between two groups that cannot speak the same language. This means translating concepts, instead of providing a literal word-for-word version.
Here is a well-known example: Pepsi wanted to translate their latest slogan to increase sales in China. "Come Alive With The Pepsi Generation" somehow ended up being presented to Chinese consumers as "Pepsi Will Bring Your Ancestors Back From The Dead."
Other cases may not only sound scary, but fatal: instructions on a medicine bottle read "Adults: 1 tablet 3 times a day until passing away." The intention was to say that the dose should be taken "until symptoms pass..."
False friends are the root of the problem
A vast majority of Western vocabulary comes from Latin and Greek origin; therefore, many words may look similar in several languages, but have completely different meanings.
These false friends can be extremely misleading. Here's an English-Spanish example: Embarrassed and embarazada may look like they share the same linguistic root, but while the former represents the emotional state experienced upon having a socially act or condition witnessed by or revealed to others, the latter actually represents the physical state of a woman carrying one or more offspring in her womb.
Another example: the word red exists in both languages, but it is a color in English and, in Spanish, it means network.
Language is a living being
Professional linguists must continuously study their working languages, because the body of spoken and written words used by native speakers is constantly evolving.
A good example is the word manufacture, which came from Latin manu factus, that is, made by hand. Nowadays, items are manufactured in large scale by machines.
Slangs have largely contributed to updates in meaning. These days, everybody says "awesome" when they see something "terrific, impressive, amazing, extraordinary." However, its original meaning was "that which has the power to inspire dread.
There are also countless words that have taken on a new meaning due to advances in technology (i.e. the computer world.) Site (physical location / internet address,) mouse (animal / small manual device that controls a cursor on a screen,) and cookie (sweet treat / small file containing personal information, created by a website server on a user's computer) are some of them.
Computers can read it, but they just don't get it
Regardless of advances in technology, computers cannot replace translators. Obviously, computers are capable of compiling extremely large databases and providing a translation for a given word or expression within a split second?and that is a lot faster than a human brain.
However, computers cannot read between the lines and interpret the shades of meaning. A software will retrieve the word señorita to replace the word miss, but it will completely ignore the fact that the original did not work as a noun, but as a verb (to miss = extrañar, echar de menos.)
It takes a lot of research
A single word may mean different things according to the context. Love may be a many splendorous thing in a romantic way, but it represents a score of zero in a tennis match.
Knowledge comes with experience and being familiar with the given field is of utmost importance. Translators with a strong background in one or more areas, as either professionals or enthusiasts, can provide a better version for an original material dedicated to that specific segment.
Speaking to a real audience
Translators are not only committed to providing their clients with the best services they can provide. They must also have the target audience in mind, for readers will be the end users of their product.
Language registers must be respected, for a highly specialized article intended to be published at a trade magazine, whose audience is comprised of doctors or engineers for example, will not use the same wording as a consumer-oriented brochure that provides information about a product or service to laypersons.