Gemara

(Beraisa): "V'Omdu Shnei ha'Anashim" cannot refer to the parties, for also women must come for judgment! If you prefer, you can learn from "Shnei."

One could have challenged the first answer, for women do not normally come to Beis Din for judgment - "Kol Kevudah Vas Melech Penimah."

31a (Rav): "Lo Tov Asah b'Soch Amav" is one who pleads on behalf of another through Harsha'ah (power of attorney).

33b (Shmuel): Witnesses are liable (for a false oath that they do not know that testimony) if someone with a Harsha'ah asked them to testify.

Chachamim of Neharde'a taught that we do not write a Harsha'ah on Metaltelim, i.e. if the defendant denied owing. If not, we may write it.

Makos 6b (Mishnah): "Al Pi Shnayim Edim" teaches that the Sanhedrin may not hear through a translator.

Two came in front of Rava who spoke (only) a foreign language. Rava put a translator between them.

Question: The Mishnah forbids this!

Answer: Rava could understand what they said. He needed the translator only to speak to them.

Bava Kama 8b (Abaye): If Reuven sold land to Shimon, even without liability if will be taken, and Reuven's creditor Levi collected it, Reuven can take Levi to Din. Levi cannot say 'you have no claim against me.' Reuven can say 'I don't want Shimon to have complaints against me (that I caused him a loss).'

Rishonim

Rif and Rosh (14b and 4:2): "Lo Tov Asah b'Soch Amav" is one who pleads on behalf of another through Harsha'ah.

Ran (DH Zeh): One who does so gets involved in others' quarrels. Perhaps his opponent would prefer to deal with the actual party, who can compromise. A Shali'ach cannot compromise money that is not his.

Ran (13b DH v'Ifligu): Early Chachamim argued about whether a defendant may appoint a Shali'ach to claim for him in Beis Din. The Aruch and R. Chananel prove that he can from the Yerushalmi. A Mishnah says that a Kohen Gadol can be judged, and he can appoint a Shali'ach. It asks, if he must swear, can a Shali'ach swear for him?! This shows that if not for the oath, the Shlichus works. They must explain that in Makos, we require the Sanhedrin to hear witnesses directly, but they may hear litigants' claims through a Shali'ach. In a Teshuvah, the Rif says that a defendant cannot make a Shali'ach. He might make false claims in Beis Din that the defendant would not have the audacity to say in front of his opponent, who knows the truth. The Yerushalmi suggested that a Kohen Gadol can make a Shali'ach, due to his honor. A regular person may not, even a distinguished woman. The Rif permitted only for Beis Din to send scribes to record her claims, but she may not claim through a Shali'ach. For a Kohen Gadol, even claiming in front of scribes is disgraceful. Also the Rambam does not allow claiming through a Shali'ach. He infers that in Makos, a translator was used for litigants (and we said that Beis Din must hear directly), for it says 'they came in front of Rava', and 'he put a translater between them.

Rambam (Hilchos Sanhedrin 21:8): A judge may use a translator only if he understands the litigants' language, but he is not fluent to answer them. He may set up a translator to inform them of the verdict and the reasons for it.

Rosh (Shevuos 4:2): The Ri ha'Levi learns from our Gemara that we do not disgrace an honorable woman to go to Beis Din, due to "Kol Kevudah." Rather, we send a Shali'ach of Beis Din to hear her claims. The Aruch and R. Chananel agree. The Ramban and Teshuvos of the Rif and Rav Sadya Gaon do not allow this. The Rif allows only that Beis Din send scribes to record her claim. The same applies to a Chacham for whom it is degrading to argue with Amei ha'Aretz in Beis Din; his honor is greater than a woman's.

Tosfos (31a DH Zeh): It is bad to accept Harsha'ah when he ia appointed because he is more likely to win in Beis Din, but it is a Mitzvah to accept Harsha'ah for a litigant who cannot come to Beis Din.

Mordechai (Bava Metzia 276): The Yerushalmi connotes that as long as the litigant swears himself, he can make a Shali'ach. Reuven can take Levi to Din, lest Shimon will have complaints against him. If not, he could not claim against him! Perhaps this is when Shimon is not here to appoint Reuven to be a Shali'ach. Avi ha'Ezri says so. Surely a Yavam cannot make a Shali'ach. If he will not do Yibum or Chalitzah, we whip him until he dies!

Poskim

Shulchan Aruch (CM 124:1): The defendant cannot appoint a Shali'ach to go to Beis Din for him to answer the claimant's claims.

Darchei Moshe (2): Neither litigant may claim in Beis Din through a translator. Since he is there, he himself must claim. If a claimant is not in Beis Din, he may claim through a Shali'ach, but a defendant may not.

SMA (1): A claimant may claim through a Shali'ach. The Chazakah that one cannot be brazen in front of his creditor does not pertain to him. Also, the claimant is Makneh (transfers ownership) to the Shali'ach, and it is as if he claims for himself. Also, it was necessary to enact that a claimant can make a Shali'ach, lest one borrow money and go overseas (and it is not worth it for the lender to go overseas to take him to Beis Din).

Shach (1): Nowadays, the custom is that the claimant claims along with another. We can explain like the SMA (17:14) said (about hearing the litigants through a translator), that whoever comes in front of fixed judges, it is as if he accepted to be judged this way. However, if so, a defendant could protest! Also, if so also a defendant could claim with another if the claimant consents! The custom is that a claimant claims along with another even if the defendant protests, but a defendant never claims with another. Rather, we permit only when he gives power and Reshus to the translator, for then he is considered a litigant. A defendant has no power to give. The Darchei Moshe says that a claimant in Beis Din cannot make a Shali'ach to claim for him, i.e. unless he gives him power and Reshus.

Shulchan Aruch (ibid): For an esteemed woman, for whom it is undignified to go to Beis Din, we send judges' scribes and she and her opponent claim in front of them. The same applies to a Chacham with no other occupation for whom it is disgraceful to go to Beis Din and argue with an ignoramus.

Beis Yosef (DH veha'Rashba): The Rashba (2:393) says that the defendant cannot make a Shali'ach to claim for him. How can one who does not know the truth say what happened?! In another Teshuvah (6:210) he sided with those who permit; if an oath is needed, the defendant himself swears if he is there. If not, Beis Din sends and they administer the oath. The Yerushalmi said that a Kohen Gadol cannot make a Shali'ach due to the oath. I.e. we cannot totally uphold his honor, for sometimes he must swear in front of Beis Din, therefore, he cannot make a Shali'ach. However, this is difficult. There are laws (e.g. one who totally denies need not swear) that depend on one's inability to be brazen (and lie) in front of his creditor! The Rambam connotes that no claimant or defendant can claim through a Shali'ach.

SMA (3): When we send scribes to a woman, the claimant may go with them, so she will be ashamed to claim falsely in front of him.

SMA (4): Here we discuss a Chacham who wants to accept the judges' verdict, but it is disgraceful for him to go and argue with an ignoramus. It is only if he has no other occupation. If not, he normally deals with Nochrim and ignoramuses, so surely he must go to Beis Din. I prefer to say that we are so concerned for the Chacham's honor to enact this for him only if he has no other occupation.

Shach (4): YD (243:2) says that a Chacham with no other occupation is one who works only for his needs, and whenever he is free he returns to learn. If so, why do we force Chachamim to come to Beis Din? We must say that this depends on custom, just like exempting Chachamim from taxes. Maharashdam says that a Kinyan from the defendant does not help. If the claimant had a Din with the defendant's Shali'ach, and the Shali'ach admitted, the defendant can retract the Shlichus and need not pay due to the admission. This is wrong. The Rivash (392) proves from the Yerushalmi that his admission is binding. The Rosh and Tur say that a claimant cannot say 'I was Mevatel my Shali'ach before he claimed for me', for he wrote that the Shali'ach can acquire for himself. Maharashdam infers that a defendant can do so. This is wrong. Even if it were right, we cannot learn from retraction from Bitul! Also, the Rosh and Tur needed to teach only about a claimant who can prove that he was Mevatel. If not, even if he did not write that the Shali'ach can acquire for himself, he is not believed to retract. All the more so, a defendant cannot retract from his Shali'ach's admission!

Note: The Rivash said that admission is binding if he appointed the Shali'ach in front of witnesses, and told them 'I accept whatever the Shali'ach will admit.' If not, the admission is not in front of witnesses.