Created attachment 127039 [details]
Comparing Kate to FeatherPad

Lines with some Asian characters have wrong height, cutting off the bottom of these characters.
Try pasting 한국어 or 日本語 and at the same line _, the bottom of the line simply disappears, it seems to be some sort of miscalculation of line height (as these characters are taller).

https://imgur.com/a/soELt03 (same text)(also available as attachment)