请参阅此链接以获得答案How to set Joi validations with custom messages?？
这是从发布的链接复制的答案。

const Joi = require('joi');

const schema = Joi.object({
        username: Joi.string().alphanum().min(3).max(16).required().messages({
            "string.base": `Username should be a type of 'text'.`,
            "string.empty": `Username cannot be an empty field.`,
            "string.min": `Username should have a minimum length of 3.`,
            "any.required": `Username is a required field.`,
          }),
          password: Joi.string().required(),
          password_repeat: Joi.any().valid(Joi.ref('password')).required().messages({
            "any.only" : "Password must match"
          })
});