Hmmmm if I remember correctly, the Japanese language file specifies a slightly larger font size, that may cause the missing space for the second line.
One idea that would not fix it, but work around it more or less, is that I was looking at the standard Windows notification that usually appears in the same area. It's not available on all Windows versions, so it would only be an alternative, but on modern Windows versions it would better 'fit in', and automatically resize depending on the content.
So, current workarounds would be to reset the Japanese font size to the standard size, or choose a sligthly shorter text for the first line (so that it wouldn't wrap, moving the second to the third). Another thing might be that I add something to update the window size relative to the font size, so that if a larger font is used, the window width at least would be scaled by that factor (9 8th).