Know your entities!
Having worked on numerous bilingual sites, I often run into accented characters and ligatures that don't work in older browsers. Entities such as ™ and œ don't work in Netscape 4. Luckily, N4's support for numerical entities is much better. ™ can be replaced with ™ and œ can be replaced with œ. Check out the W3C's list of character entity references in HTML 4 or I use Blooberry's which details browser compatibility for each character.