If your app has Japanese users — or wants them — there's a bug class your English-speaking team will almost never hit, and Japanese users hit in the first five minutes.

How Japanese input actually works

Japanese text goes through an IME (Input Method Editor). You type romaji, the IME composes candidates, and you press Enter to confirm the conversion — not to submit. That Enter is part of typing.

If your app treats that Enter as a submit/commit event, you've broken typing itself.

Real examples (all public)

• NocoDB — pressing Enter to confirm a Japanese IME conversion also got interpreted as "create a new record," so typing a cell value became a minefield. (nocodb/nocodb#10394)
• Chatwoot — an IME bug in the AI reply field broke Japanese composition in the support UI.
• Twenty CRM — a Unicode bug rendered Japanese text as raw escape sequences in field display.

A monolingual team can ship for years without triggering any of these. A Japanese user hits them immediately — and most won't file an issue. They'll just leave.

Check your own app (2 minutes)

1. Switch your OS input to Japanese (or use the on-screen IME).
2. In any field with an Enter/submit handler, type a few romaji and press Enter to confirm the conversion — before you mean to submit.
3. If that Enter submits the form / creates the record / sends the message, you have the bug.

The fix is small: check event.isComposing (or keyCode === 229) and ignore Enter while a composition is active.

input.addEventListener('keydown', (e) => {
  if (e.key === 'Enter' && (e.isComposing || e.keyCode === 229)) return; // IME confirm, not submit
  if (e.key === 'Enter') submit();
});

IME is one of five

It's the most visible JP-readiness gap, but it's one of five that quietly leak Japanese users before they show up in your analytics:

1. English-only funnel (the ja locale exists; the path to it is English)
2. No 特商法 (Tokushoho) page — the expected legal disclosure for selling in Japan
3. USD-only pricing
4. Invisible in Japanese category search
5. IME / CJK input bugs

I scored 13 open-source dev-tools on these five dimensions, each gap linked to a real GitHub issue or live URL. The index is free: https://jp-ready.glovrex.com

Want a scan of your own product? https://glovrex.com/check — enter your URL, get the five-signal check.