Halakhah su Numeri 30:3

And regarding a vow (neder), a different approach pertains to it - as it is like placing something permissible into the category of the forbidden, and [it is] as if he would say thing x which is permissible will be forbidden to him, like a sacrifice that God, may He be blessed, forbade. And they, may their memory be blessed, said (Nedarim 14a) that only when he makes the vow with a thing that is vowed (that changes status) does his vow stand, and not in another way. As if he says, "Thing x is forbidden to me like a sacrifice," as we have said; in this [way], the vow will stand (Nedarim 13a). But if he says, "like the meat of a pig," this is not a vow; as the Torah stated (Numbers 30:3), "If he vows a vow," meaning to say, "if he vows with something that is vowed." And so, one who forbids something to his fellow or to himself like the matters of a sacrifice that God, may He be blessed, forbade, is like this matter (like something vowed); since it is as if he said [that] thing x will be forbidden to him or to his friend, [just] like God, may He blessed, forbade us the matters of a sacrifice. And this matter that we have the power to forbid the permissible is because the Torah taught us this, from that which is written (Numbers 30:3), "If [...] he creates a prohibition [...], he may not break his word."

The general principle of the thing is that the language of the oath must be said by his own mouth or that someone else specifically refers it to him and he accepts [it]. But he is not moved by the movement of another man, since his [own] body needs the movement; [but this] is not the case with a vow. [It is also] possible to say that it is from the strictness of a vow that they were stricter about it, that one should be added on more quickly than with an oath; since it is stricter than an oath, as behold, they compare it to the life of the King (Sifrei Bamidbar 123:3, see Ramban on Numbers 30:3). And from the reason that we wrote about an oath, that its content is that a man concludes to fulfill his words and to confirm [them by that which] he believes in the Divine existence, we would have learned that his oath cannot be nullified from any angle. But it was from the kindnesses of God to us - in His knowing the frailty of the structure of our body and the smallness of our opinions and the constancy of the change of our wills - to give us counsel to get out from the prison of the oath with the [change] of our will at any time: he allowed us to make the claim regarding the matter of the oath that it was under duress or inadvertent, as is explained in its place in Shevuot 26a and Nedarim 20b.

It is customary to do hataras nedarim [to annul certain vows] on erev Rosh Hashanah. (An allusion [for this can be found in the words] Lo yacheil devaro kechol, [He must not break his word (Numbers 30:3)]; the last letters of which form the acronym Elul.) A person who does not understand what he is reciting in Hebrew, should say it in the language he understands.