CJK Language Support

Streamdown includes built-in support for CJK (Chinese, Japanese, Korean) languages, ensuring that emphasis markers like bold and italic work correctly with ideographic punctuation. This is particularly important for AI-generated content, where language models naturally place emphasis markers around phrases that include or end with punctuation.

The Problem

The CommonMark/GFM specification has a limitation where emphasis markers (** or *) adjacent to ideographic punctuation marks occasionally fail to be recognized. This causes formatting to break in CJK text:

**この文は太字になりません（This won't be bolded）。**この文のせいで（It is due to this sentence）。

Without CJK-friendly parsing, the text above would render as plain text instead of bold because the closing ** appears next to the Japanese period.

The Solution

Streamdown uses the remark-cjk-friendly and remark-cjk-friendly-gfm-strikethrough plugins to handle CJK text properly. This plugin implements an improved parsing approach that correctly recognizes emphasis markers adjacent to ideographic punctuation.

Supported Features

Bold Text with Punctuation

Works correctly with all ideographic punctuation marks:

**日本語の文章（括弧付き）。**この文が後に続いても大丈夫です。
**中文文本（带括号）。**这句子继续也没问题。
**한국어 구문(괄호 포함)**을 강조.

Japanese: 日本語の文章（括弧付き）。この文が後に続いても大丈夫です。

Chinese: 中文文本（带括号）。这句子继续也没问题。

Korean: 한국어 구문(괄호 포함)을 강조.

Italic Text with Punctuation

*これは斜体のテキストです（括弧付き）。*この文が後に続いても大丈夫です。
*这是斜体文字（带括号）。*这句子继续也没问题。
*이 텍스트(괄호 포함)*는 기울임꼴입니다.

Japanese: これは斜体のテキストです（括弧付き）。この文が後に続いても大丈夫です。

Chinese: 这是斜体文字（带括号）。这句子继续也没问题。

Korean: 이 텍스트(괄호 포함)는 기울임꼴입니다.

Strikethrough with Punctuation

Streamdown includes remark-cjk-friendly-gfm-strikethrough for proper strikethrough support:

~~削除されたテキスト（括弧付き）。~~この文は正しいです。
~~删除的文字（带括号）。~~这个句子是正确的。
~~이 텍스트(괄호 포함)~~를 삭제합니다.

Japanese: 削除されたテキスト（括弧付き）。この文は正しいです。

Chinese: 删除的文字（带括号）。这个句子是正确的。

Korean: 이 텍스트(괄호 포함)를 삭제합니다。

Mixed Content

CJK and English text work seamlessly together:

**重要提示（Important Notice）：**请注意。

Result: 重要提示（Important Notice）：请注意。

Supported Punctuation

The plugin handles all common ideographic punctuation marks:

• Parentheses: （）
• Brackets: 【】「」〈〉
• Periods: 。．
• Commas: ，、
• Questions: ？
• Exclamations: ！
• Colons: ：

Why This Matters for AI

Language models generate markdown naturally, often placing emphasis markers around phrases that include punctuation. Without CJK-friendly parsing, AI-generated content in Chinese, Japanese, or Korean would have broken formatting.

❌ Without CJK support:

• The model writes: **この用語（読み方など）**について説明します。
• The user sees: **この用語（読み方など）**について説明します。 (not bold!)

✅ With CJK support:

• The model writes: **この用語（読み方など）**について説明します。
• The user sees: この用語（読み方など）について説明します。 (properly bolded!)

## Configuration

CJK support is enabled by default with no configuration required. The plugins are included in the default remark plugin list:

```tsx
import { Streamdown } from "streamdown";

export default function Page() {
  return <Streamdown>{markdown}</Streamdown>;
}

Disabling CJK Support

If you need to disable CJK support, you can override the default remark plugins:

import { Streamdown } from "streamdown";
import remarkGfm from "remark-gfm";
import remarkMath from "remark-math";

export default function Page() {
  return (
    <Streamdown remarkPlugins={[remarkGfm, remarkMath]}>{markdown}</Streamdown>
  );
}

Note: This removes all default remark plugins, so you'll need to add back any others you need.