The following excerpts are from Brave new words blog:

The following are some of the reasons why you might want to get a PhD in translation:
–You want to go into academia. In most cases, you will need a PhD to get an academic job.

–You have a passion for a particular subject and want to explore it in depth. This is what a PhD is about.

–You want a qualification that will help you stand out from other translators. I know a number of translators with PhDs and they certainly say that in a glutted market, any extra qualifications or skills can help you get work instead of someone else.

–You want a qualification that will help you stand out from other writers. Some people get a PhD because they then want to write “the” book on a particular subject. Many PhDs do lead on to books based on the thesis/dissertation and having another qualification will help ensure a publisher that you are the right expert for the book.

–You love learning and would thrive in an academic environment for a number of years. Some people really enjoy attending classes, seminars, and workshops, spending time in the library, debating and discussing ideas with others, and so on. If that’s you, then getting another degree might very well suit you.

See: Brave new words