Support Node SimpleSchema validation messages i18n using TAPi18n package. Reactively depends on TAPi18n.getLanguage() on the Client.

meteor add imajus:simple-schema-i18n

And, if tap:i18n is not in the project yet:

meteor add tap:i18n

1. Fetch SimpleSchema MessageBox messages translation for each langauge from TAPi18n.getLanguages() on Meteor.startup().
2. (Client only) All SimpleSchemai18n instances depend reactively on TAPi18n.getLanguage().
3. Extend schema options with { tracker: Tracker } so you don't need to provide this option to every SimpleSchema constructor call anymore.
4. Initially extend SimpleSchema with ['autoform', 'denyInsert', 'denyUpdate'] options.
5. Set SimpleSchema.debug to Meteor.isDevelopment.

i18n/en.i18n.json

{
  "simple-schema-i18n": {
    "required": "{{{label}}} is required"
  }
}

Example, you actually need to fill the "simple-schema-i18n" section with all messages.

i18n/ru.i18n.json

{
  "simple-schema-i18n": {
    "required": "{{{label}}} обязательное поле"
  }
}

Example, you actually need to fill the "simple-schema-i18n" section with all messages.

project-tap.i18n

{
    "helper_name": "_",
    "supported_languages": null,
    "i18n_files_route": "/i18n",
    "cdn_path": null,
    "preloaded_langs": ["*"]
}

Here, "preloaded_langs" option is crucial for package to work properly. Other options could be changed as you like.

import { SimpleSchema } from 'meteor/imajus:simple-schema-i18n';

const schema = new SimpleSchema({ /* Fields definition */ });

const message = { type: 'required', label: 'Field' };
console.log(schema.messageBox.message(message, { language: 'en' }));
// Output: Field is required
console.log(schema.messageBox.message(message, { language: 'ru' })); 
// Output: Field обязательное поле

/**
 * Уou can use this SimpleSchema as usual, the language of validation errors
 * will reactively depend on TAPi18n.getLanguage() and change accordingly.
 */

Let's assume your current code look like this:

import { Tracker } from 'meteor/tracker';
import SimpleSchema from 'simpl-schema';

const schema = new SimpleSchema({ /*…*/ }, { tracker: Tracker });

To support SimpleSchema i18n, the code above must be change to this:

import { SimpleSchema } from 'meteor/imajus:simple-schema-i18n';

const schema = new SimpleSchema({ /*…*/ })

Obviously, you also need to add tap:i18n Meteor package dependency and create actual i18n files.

For some reason I couldn't embed initial translations in package itself. TAPi18n currently doesn't work well on package level, and as far as I can see package author is not willing to fix any bugs in the nearest future. That's why I've switched to project level i18n files instead.