no-language-mixing

Disallow mixed-language tokens combining latin and non-latin letters.

Targeted pattern scope

This rule checks string literals and template literal raw segments.

It reports tokens that mix latin letters with non-latin letters in the same word-like segment.

What this rule reports

This rule reports string and template content where latin and non-latin characters are mixed in one token.

Why this rule exists

Mixed-script tokens can hide confusable text and reduce readability in internationalized codebases.

❌ Incorrect

const x1 = "яz";
const x2 = "xyz123абв";

✅ Correct

const x = "xyz";
const y = "123";
const z = "абв";

Behavior and migration notes

This rule reports only and does not provide an autofix.

Migrate by separating scripts per token or using one script consistently.

Options

This rule has no options.

Additional examples

const message = `пользователь id42`;
// ✅ each token is single-script or numeric

const mixed = `пользовательId42`;
// ❌ reported (mixed script token)

ESLint flat config example

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/no-language-mixing": "error",
  },
 },
];

When not to use it

Disable this rule if mixed-language tokens are expected and accepted in your project.

Package documentation

• eslint-plugin-etc-misc README

Rule catalog ID: R030

Further reading

• Unicode Standard
• MDN: String

Adoption resources

• Start at warning level in CI, then move to error after cleanup.
• Use focused codemods/autofix batches per package or directory.