We have dealt, in the past, with different elements of the process of testimony. Let us now give some thought to the question of how witnesses testify in practice. Normally they are to testify while physically before beit din in a standing up position (although an issue is not usually made about the latter). We will now look into the question of when a witness does not have to testify in the classical way, specifically: when someone else can present his testimony, when he can testify through a translator, and when he can testify in writing.
The mishna (Sanhedrin 37a) says that beit din warns the witnesses regarding capital cases: "Perhaps you are relating based on assumption or rumor, or you heard testimony, one witness from another or from a reliable person." The gemara (ibid. 37b) says that the inadmissibility of an account coming from someone else applies to monetary law as well. The exception to this rule is when the first testimony was related to a beit din, in which case, the dayanim or others present in court may repeat the information in front of a different beit din. According to many authorities, this is only when the first beit din determined that the testimony was accurate. Another exception is that witnesses can testify about what they saw in a valid document, which is of value if the document was subsequently erased or destroyed [regarding written testimony, in general, see next week].
Based on this, when a witness is in a distant location, beit din can send three dayanim to the witness to hear his testimony, and they can later testify on that which they heard from him. According to almost all opinions, there must be three people accepting the testimony; one representative of the court is insufficient. Therefore, a simple notarized statement does not have a special halachic standing.
Regarding hearing testimony through a translator, the mishna (Makkot 6b) says that it is not valid. However, the gemara says that if the dayan understands the language reasonably and needs a translator only to communicate his questions to the witness, it is permitted to do so. The Radvaz says that the disqualification of hearing through a translator is only rabbinic, and therefore if there is no dayan available who understands the witness, a translator may be used. This, though, is still talking about a case where the witness speaks and the translator translates in front of beit din. If the translator alone comes to court to relay testimony, that is actually a case of one testifying in the name of another, which, we saw, is invalid.