[iOS] TextInput fontFamily issue with some keyboards in iOS

Description

I'm not sure what the main cause of the issue is, but I ran into an issue with CJK keyboards in iOS, that the fontFamily is not set correctly.

const [text, setText] = useState("");

const fontFamily = !text ? "ZenMaruGothic" : "IMHyemin";

return (
  <SafeAreaView>
    <View style={styles.view}>
      <TextInput
        multiline
        defaultValue={text}
        onChangeText={setText}
        placeholder="フォントテスト"
        style={[styles.textInput, { fontFamily }]}
      />
     {/* ... */}

When the text is typed on keyboards having "pending states" . That is, the state in which the text can be modified by the additional keystrokes and confirmed by the user to be finalized. Examples include:

• with the Chinese pinyin keyboard, one types nh and selects 你好 to finalize the input
• with the standard Korean (qwerty) keyboard, keystrokes ㄱㅏ yield 가 (U+AC00) in its pending states, and an additional keystroke ㄴ modifies it to be 간 (U+AC04)

As you can see in the video, when typed using the standard English keyboard, at the first keystroke, the letter is correctly styled with the provided font. But using Chinese/Japanese keyboards, the first keystroke does not change the font and the following keystrokes change it. Even worse, using the Korean keyboard, the font of the TextInput is not changed at all.

Steps to reproduce

Expo snack: https://snack.expo.dev/@kanukim/textinputfonttest

Issues with Korean characters:

1. Open the project in an iOS device
2. Add a Korean Keyboard (Standard)
3. Type "한글" (FYI, you can type it by pressing ㅎㅏㄴㄱㅡㄹ in sequence)
4. The fonts are not set correctly (as the text input below)

You may test the issue with various keyboards including Japanese (romaji) and Chinese (pinyin) inputs.

React Native Version

0.76.3

Affected Platforms

Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx react-native info

System:
  OS: macOS 15.1.1
  CPU: (8) arm64 Apple M1
  Memory: 206.56 MB / 8.00 GB
  Shell:
    version: 3.7.1
    path: /opt/homebrew/bin/fish
Binaries:
  Node:
    version: 22.9.0
    path: ~/.local/share/nvm/v22.9.0/bin/node
  Yarn:
    version: 1.22.22
    path: ~/.bun/bin/yarn
  npm:
    version: 10.8.3
    path: ~/.local/share/nvm/v22.9.0/bin/npm
  Watchman:
    version: 2024.09.09.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.14.3
    path: /usr/local/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.1
      - iOS 18.1
      - macOS 15.1
      - tvOS 18.1
      - visionOS 2.1
      - watchOS 11.1
  Android SDK:
    API Levels:
      - "33"
      - "34"
    Build Tools:
      - 30.0.3
      - 33.0.0
      - 33.0.1
      - 34.0.0
    Android NDK: Not Found
IDEs:
  Android Studio: 2024.1 AI-241.18034.62.2411.12071903
  Xcode:
    version: 16.1/16B40
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.12
    path: /opt/homebrew/opt/openjdk@17/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 16.0.0
    wanted: latest
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.3
    wanted: 0.76.3
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

No errors

Reproducer

https://snack.expo.dev/@kanukim/textinputfonttest

Screenshots and Videos

https://github.com/user-attachments/assets/dbd6a83a-4f22-45c3-aa61-f17c8c53f7bf

Please focus on the missing font changes at the first keystrokes.

Start with the linked Expo Snack and reproduce the issue on iOS using English, Chinese pinyin, Japanese, and Korean keyboards. Investigate the Fabric TextInput behavior around pending composition states; the issue is done when fontFamily changes on the first relevant keystrokes and remains correct for finalized CJK input.