Because there are many Latin phrases in the law, many people believe that lawyers at one time spoke Latin. The truth is more complex.
There is no period in English history in which Latin would have been spoken in court (except an ecclesiastical court). Educated people spoke French; the rest spoke English (what we would now call Middle English). The language used by the litigants and witnesses, whether French or English, was translated before it was recorded in the records of the proceedings.
The language in which they are written is that thought appropriate for formal records. Early on that was Latin; by the thirteenth century it was a combination of Latin, French, and English called Law French. This is one reason why the case records are not verbatim transcripts, although they often look like it. Another reason is that exact wording — whether in transcripts, laws, or writs — was not felt to be critical; getting the gist right was what counted. In the oral tradition, the mindset of which was still strong, there was no feeling that the restatement of a person’s utterance had to be a word-for-word reproduction of it.
Legal writs continued to be written in Latin. When read aloud, however, they were translated into language the litigants could understand. In court this was normally French; when town criers announced the promulgation of new laws they translated them into English.