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"The Japanese Is Disappearing" — What Bilingual Research Actually Says About Heritage Language and Re-entry

By Leon MoriguchiPublished May 15, 2026Updated May 18, 20265 min read日本語版あり
Audience
Parents living abroad who are worried about their child's Japanese; parents preparing to return to Japan

TL;DR

  • ·Cummins's Linguistic Interdependence Hypothesis — tested across multiple language pairs — shows that strong L1 academic proficiency supports L2 development, not the reverse; building strong Japanese does not come at the cost of the host-country language
  • ·The gap returnee children face is primarily written literacy — kanji, composition, academic register — not spoken fluency, which tends to persist reasonably well even across extended overseas periods
  • ·Supplementary Japanese school attendance (one to two sessions per week) has documented effects on written-language retention; assessing written Japanese ability before returning to Japan, rather than after, allows more time to prepare

Contents

  1. Lead
  2. "Learning one language blocks the other" — the claim that doesn't hold
  3. Japanese as a heritage language
  4. The literacy gap on return to Japan
  5. Language and identity
  6. Putting it into action
  7. Summary
  8. References

Lead

"What if the Japanese just disappears?" is an anxiety that many parents raising children abroad recognize. Once a child starts at the local school, the host-country language accelerates visibly — while Japanese vocabulary seems to shrink, and a child who was spoken to in Japanese starts answering in the local language.

Language-acquisition research has accumulated reasonably clear findings on this question. The reassurance comes with conditions, though: there are identifiable factors that support heritage language maintenance.

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