Japanese speakers
Mistake: Pronouncing it as "SANKYU" with a Japanese [s] (or worse, [ts]) replacing the [θ], and dropping the fusion entirely.
Why: Japanese has no [θ] sound. Katakana "サンキュー" replaces it with [s], and the pop-culture spelling reinforces the wrong articulation.
Fix: Put the tip of your tongue lightly between your teeth for the [θ] — no voice, just air. Then the k + y at the boundary softens toward [kj], giving [ˈθæŋkjə] in fast speech. The final "you" reduces to [jə], not [juː].
Korean speakers
Mistake: Substituting [s] for [θ] (like "SAENK YU") or preserving the full [ju:] vowel with a clear syllable break.
Why: Korean has no [θ] sound, and Korean politeness registers favor careful, unreduced vowels.
Fix: The [θ] is the same as in "think" — practice "think you" and "thank you" back to back. In natural speech "you" reduces to [jə]: [ˈθæŋkjə]. The politeness is carried by warm intonation, not by full vowels.
Chinese speakers
Mistake: Producing a strong [s] for [θ], or over-emphasizing the k with aspiration ([kʰ]), making it sound choppy.
Why: Mandarin has no [θ]; the closest substitute is [s]. And Mandarin voiceless stops carry strong aspiration by default.
Fix: [θ] requires the tongue between the teeth — no substitution works well. Keep the k light and let it flow into a reduced [jə]: [ˈθæŋkjə].