In order to select a language, you can select any 2 languages of your choice depending upon how comfortable you are while working in it. After a thorough study of two languages, you can also move forward to learning more languages which also is your choice completely. 
In written translation, a translator is required to translate a written text or document in another language. The text can be any official document, letter, notices issued by the government, notes, study material of various fields of education, literary works, and a lot more. 
In oral translation, most of the time the translator is required to translate a speech live. They also sometimes translate recorded audios and videos. The speeches could be political, educational, etc. And require on the spot precise translations. 
The key to a successful career in translation is your work of translation whether written or oral is supposed to be clear, accurate, and concise, without altering the meaning of the text. It should also be understandable by the readers or listeners. 
Oral translators are also bound to time limits and must have the skill to translate any sentence or word quickly within seconds, without changing its meaning. 
You can also take up courses on translation for specialized training, certification, and deeper knowledge and experience in the field. There are also various language courses that can come in handy in learning a language. 
You can also start freelancing in order to gain some experience in the field.  That will help you take up your dream translation job. 
 
Although in demand, the job of a professional translator requires a lot of skill and a thorough knowledge of atleast two languages.