Why does typing in Chinese, Japanese or Korean show underlined text on iPhone?
The grey underline that shows up while you are typing pinyin, romaji or Hangul jamo is not a spelling flag and not a font style — it is marked text, iOS’s way of showing a character that has not actually been entered yet. What it means, why only these three languages need it, and when it disappears.
You are typing pinyin, or romaji, or a string of Korean jamo, and for a second the letters sit there with a thin grey line underneath them — the same visual cue used elsewhere for a typo. Then you tap a candidate, or hit space, and the underline vanishes along with the letters it was under, replaced by a real Chinese character, a hiragana word, or a finished Hangul block. Nothing was wrong. That underline is not iOS flagging a mistake. It is the system showing you something you typed that has not actually been entered into your message yet.
It is marked text, not a mistake
Every text field on iOS distinguishes between two kinds of content: committed text, which is the real content of the message, note or search box, and marked text, which is a temporary, still-editable draft sitting on top of it. Marked text is not yet part of what you are writing — it is what the keyboard currently understands you to be in the middle of typing, and it can still be changed, replaced or thrown away before it becomes real. iOS underlines marked text specifically so the two are easy to tell apart at a glance, the same way a photo editor might dim a layer that has not been flattened into the image yet.
This is not something a keyboard app invented. It is a standard part of how iOS handles text input, available to any keyboard, and it exists because some languages genuinely need a “still deciding” state that plain typing on a Latin keyboard never does.
Why only three of Kibo’s 30 languages ever show it
Type an “e” on an English keyboard and it is final the instant it appears — there is nothing left to decide, so there is nothing to mark as provisional. Three of the languages built into Kibo work differently, because a single keystroke there is not automatically a finished, committed character. Chinese Pinyin turns a romanised sound into a list of character candidates you have not chosen between yet. Japanese Romaji turns a sound into hiragana that might still be converted into kanji. Korean assembles individual jamo into a syllable block that can keep reshaping as you add more strokes. All three need somewhere to hold “typed, but not yet decided” — and marked text, shown underlined, is that place.
Chinese: the underline holds a sound, not a character yet
Type “nihao” and the romanised letters themselves sit underlined above the candidate bar while it fills with 你好 and other matches. Nothing about 你好 exists in your message at that point — the underlined text is still just the sound you spelled out, waiting for you to tap the character it stands for. Tap a candidate and the underlined pinyin is replaced outright by the character; the pinyin itself never gets sent anywhere.
Japanese: the underline holds hiragana that might still become kanji
Type “kanji” with the Romaji input method and か ん じ appears underlined immediately, converted from the Latin letters, but still marked rather than committed. That hiragana might be exactly what you want to send as-is, or it might be a stepping stone toward the kanji 漢字 offered in the candidate bar above it. The underline is what lets you keep that option open — tap a kanji candidate and the underlined hiragana is swapped for it; tap space or move on and the hiragana commits unchanged.
Korean: the underline covers a block that can still change shape
A Hangul syllable block is built live, one jamo at a time, and a block that looks finished can still get pulled apart if the next thing you type is a vowel that needs a consonant to attach to. While that is still possible, the block sits marked and underlined rather than committed, because iOS genuinely cannot be sure yet whether ㅁ belongs to the block you just finished or the one you are about to start. It settles, and the underline disappears, the moment you type something that can no longer reach back and change it.
Why this never happens typing English, Spanish, French or German
Every one of Kibo’s other 27 languages types the same way English does: one keystroke, one final letter, nothing provisional about it. There is no candidate to choose between and no block that might still reshape, so there is nothing for the system to hold in a marked, editable state in the first place. The underline is not a feature some languages have and others lack — it only ever appears for languages where a single keystroke genuinely is not yet a finished answer.
What happens if you send or switch away before it settles
Marked text does not just sit there forever waiting on you. iOS commits it — turns it into real, final content — the moment you do something that is not part of continuing to compose it: tapping a candidate, pressing space or return, or moving the cursor and tapping elsewhere in the field. Tapping Send in Messages while pinyin, romaji or a jamo block is still underlined generally commits whatever is currently marked before the message goes, rather than sending the raw, unconverted letters — which is worth knowing if you have ever sent a message and wondered why it looks slightly different from what you thought you tapped.
Not the same underline as a spelling flag
It is easy to confuse this with Check Spelling’s red squiggle, since both use an underline to say “this is not settled yet” in some sense — but they are unrelated mechanisms with different purposes, covered in more detail in the guide on why iPhone underlines correctly spelled words. A spell-check squiggle sits under text that is already fully committed and stays there until you fix the word or dismiss it; marked text sits under text that was never committed in the first place and disappears the instant it either becomes real or gets thrown away. One is a note about a word already in your message. The other is the message not being finished yet.
Where Kibo fits
Chinese, Japanese and Korean are three of the 30 typing languages built into Kibo, and all three use this same marked-text mechanism — it is part of iOS itself, not something a keyboard app can change or skip. Composing text is drawn and tracked entirely on the keyboard, with nothing sent anywhere and no clipboard involved, so it works the same with Full Access left off. Kibo is free to download.
Frequently asked questions
Is the underlined text while typing Chinese, Japanese or Korean a mistake?
No. It is marked text — iOS’s way of showing a character or word that has been typed but not yet committed to the message. It is unrelated to spelling and disappears on its own once you pick a candidate or keep typing past it.
Why does this only happen with some languages and not others?
It only appears for languages where a single keystroke is not automatically a finished character — Chinese Pinyin, which offers character candidates for a typed sound, Japanese Romaji, which converts to hiragana that may still become kanji, and Korean, which assembles jamo into syllable blocks that can still reshape. Alphabetic languages like English or Spanish commit each letter immediately, so there is nothing to mark.
Does which keyboard app I use change how this underline works?
No. Marked text is a standard part of iOS’s own text input system, available to any keyboard that offers these languages, not a design choice a particular app makes. Any keyboard with Pinyin, Romaji or Hangul input handles it the same way.
Try it on your own keyboard
Kibo is a free custom keyboard for iPhone with real mechanical key sounds, a wardrobe of themes and RGB backlight effects. No account, no ads, and it works with Full Access left off.