Short definition
The B-language is an interpreter's first foreign language – a language they speak at near-native level and into which they can actively interpret.
Detailed explanation
After the A-language comes the B-language: it is an interpreter's strongest foreign language, acquired through years of intensive study and use – often through time spent abroad, university studies or professional experience in a foreign-language environment. Interpreters actively work into their B-language, although it requires somewhat more cognitive effort than interpreting into their A-language.
In practice, the line between A- and B-language can sometimes be blurred. What matters is that, in their B-language, the interpreter can do more than simply communicate: they must be able to formulate, vary their style and use precise technical terminology under simultaneous conditions. That is a demanding standard.
For conference technicians and planners, the B-language is relevant because it broadens an interpreter's range of deployment. An interpreter with German as their A-language and English as their B-language can interpret from French (C-language) into both of their active languages – which makes them more flexible to deploy.
Relevance in this field
The B-language extends an interpreter's language combination and reduces the need for additional booths. It is a key criterion when selecting interpreters for multilingual conferences.
Practical example
An interpreter with French as her A-language and German as her B-language is working at a German-French economic summit. She interprets from German into French – taking the load off her colleague in the opposite booth.