How many languages do you know and how/why do you know them? Do you recommend to concentrate on one language (other than your first language) or learn more languages which would give more work offers I guess.
I just got this question from a student wishing to pursue studies in interpreting. This is probably the most common question from students. And the answer is not as straightforward as the question (what else?). First of all you need to know your mother tongue very well. It seems obvious, but speaking a language and interpreting into a language are two very different things. When you interpret into a language you need to master all domains, all registers, and all nuances. It is so much more than just speaking your mother tongue or being fluent in a language.
How well you have to master your other languages and how many languages you “need” depend on where you aim to work. Interpreters can be “bi-active”, meaning that you master two languages equally well and work to and from both languages. In that case you have two mother tongues or you are very near native in your foreign language (an A or B-language for interpreters). Bi-active interpreters work for NATO, for courts, as conference interpreters or as community interpreters. It is more or less impossible to be bi-active in more than two languages.
Most interpreters who work for larger institutions such as EU or UN work only into their mother tongue and from at least two, but often three or more languages. The languages you work from are languages you comprehend fully, but which you do not master as mother tongue. In interpreting lingo these languages are called C-languages.
So, you cannot say that its better to focus only on one language or several. It depends on what you would like to focus on. And it also depends on whether you have a second mother tongue or a language in which you are near native. So more languages does not necessarily mean more work offers either. However, a language combination with very high demand in your region will most likely give you more work offers. Also, if you are the only one with two very rare languages you will probably have a stable market.
Personally, I work from English, French and Danish into Swedish. I work to and from English in court but not in conferences. The reason for my language combination is that I only have one first/ A/ mother tongue language and I work mostly for the EU. I am almost near native in English and therefore I work in court to and from English, I have not developed my English into conference use. You can read more about me and my languages here.