Cannot get epub to display with hyphenation

Hey guys,

I am converting a DOCX file with justified text and hyphenation (Bulgarian language) to EPUB, but when viewed in any EPUB viewer, there is no hyphenation at all.

How does it work exactly? Since EPUBs flow, there is no way the line breaks are hard coded. So is it dependent on the viewer app? Is it a matter of dictionaries? How do I make it work? Can I at all?

Thanks.