A: We convert documents from one language into another.
A: Translation is by definition in writing; the spoken task is called interpretation. I currently offer only translation and editing, not interpreting.
A: Some do. Many translators have an academic background or prior (or simultaneous) career in a particular field. Plenty of doctors and lawyers veer into translation. Others learn translation skills first and then build subject matter knowledge in something they are interested in. Specializations may be all over the map – from climbing gear to HVAC to recipes.

A: Briefly, agencies tend to offer a larger suite of services or language combinations than a freelancer. For example, if you have an English website and would like it translated into 10 languages, an agency may be the right choice. The agency will manage the project for you as well.
The flip side is that an agency will often be more expensive than a freelancer, since agency overhead and staffing costs are higher, and you probably won’t be in direct contact with whoever actually translates your documnent. Working with a freelancer, you know exactly who is translating your document and can collaborate with the person directly. Freelancers are often more flexible, able to fulfill changing requirements and incorporate feedback. Additionally, some freelancers work in networks or partnerships to offer capabilities similar to an agency’s (multiple languages, project management, etc.).

A: Yes – in the US it is the American Translators Association. There is a lot of great information on their website! Many countries have their own professional associations, especially in Europe where the profession is more standardized.
A: Yes and no. It depends what the subject is and what your translation will be used for. To figure out the general subject of a document for your own use, Google Translate (GT) might work. To translate dosing instructions for a drug, an adverse event report for a clinical trial, or marketing materials for your website, GT isn’t going to cut it. Actually, using GT could significantly damage your reputation, scare off customers, or even get you in trouble with regulators. Test it out: Put some of your high-stakes material like drug dosing instructions into GT and see what comes out. If you don’t read a foreign language, then translate it back into English and see how it differs from the original. You will be surprised.
A: In some fields, yes. It can be quite attractive in terms of cost and speed. In other fields, such as patent translation or advertising, it is a far cry from replacing humans. MT has made great strides in the last decade or so, and some systems have become quite good. I find the best way to think of it is this: a machine does not “understand” anything. When it “translates” a text, it is matching source and target language patterns based on large amounts of data that have been entered. So the machine isn’t actually “understanding” any of the text in the way that a human would. Some texts might be translated passably in this way, but texts requiring thought, consistency, stylistic decisions, or subject matter knowledge will most likely require a sentient translator.