Lawyer-linguists are always Administrator (AD) level officials who may even be recruited at a higher level (AD7 instead of AD5) to attract the most possible candidates - the condition being that they must stay in their position for at least three or more years without being able to transfer to other EU institutions or positions. A legal diploma is required, along with the knowledge of at least two or three languages at a very high level so that they can carry out translations and revisions from multiple source languages. Lawyer-linguists generally work for the Council of Ministers, the European Court of Justice or the European Parliament, though some other institutions may employ a few of them as well.
See also:
Administrator | Lawyer | Translator | Interpreter | Council of Ministers | European Court of Justice
Related link:
Language Requirements | Selection and Recruitment | Reserve List