@Ithuriel_06: Like everyone said, not enough info to guess what could have gone wrong.

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@chcheng_rwth: Probably an issue with your font (bearings/ascent/descent) [bear in mind that the Kindle's not really optimized for displaying CJK characters, so when I say 'issue', I mean 'incompatibility with the Kindle software' ^^]. You might still want to try an FT override (authint/light most likely) and see if it helps, though.