When an invoice containing Asian characters gets exported into PDF format, layout may be corrupted and instead of Asian characters unreadable symbols may appear. This happens because fonts used in default templates do not contain all the necessary glyphs to display the Unicode text.
To fix this issue, it is needed to clone any predefined invoice template and apply another font to all labels. For example, it is known that Arial Unicode MS font displays Asian characters correctly. Also, you may use any other font which has necessary glyphs.