Japanese speakers
Mistake: Pronouncing it as "WEN YU" with clear syllable break and full [ju:] vowel.
Why: Katakana English preserves each word.
Fix: The n of "when" links smoothly to the y of "you", and "you" reduces to schwa: [wɛnˈjə]. Note: unlike d+y or t+y, n+y does NOT coalesce — they stay as separate sounds.
Korean speakers
Mistake: Producing full [ju:] and syllable break.
Why: Korean maintains vowel qualities.
Fix: n + y stays as [n + j] (no coalescence) and "you" reduces to [jə]: [wɛnˈjə]. Same non-fusion as "can you" [kənˈjə].
Spanish speakers
Mistake: Producing Spanish [j] with friction, or preserving full [ju:].
Why: Spanish [j] is stronger; Spanish preserves vowels.
Fix: English [j] is light and glides smoothly: [wɛnˈjə]. Trust the schwa reduction on "you".