Which tones are hardest, why, and where to start.
Russian speakers' core problem is Tone 2: they produce it with a CONCAVE (dent-shaped) contour — measured pitch values like 113, 114 and 213 — so it loses its rise and is heard as Tone 3, making T2 and T3 hard to tell apart. Their tones are also shorter in duration than native speakers', with a lower and narrower pitch range.
Source: 高玉娟, 李宝贵 (2018). 对俄语背景者汉语声调习得偏误的实验研究. 《云南师范大学学报（对外汉语教学与研究版）》16(5), 18–26. | 《xbcrjyxb》2019(3)（万方收录） | 《汉字文化》2025(3)
Group averages tell you where to look, not what you actually do. Two speakers of the same first language can differ a lot. The only way to know is to record yourself and compare.
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