RTW is quite capable of reading the lower 1K or so characters of the Basic Multilingual Plane; and RTW enforces fonts which support rendering of characters in the BMP more than sufficiently for the current EB descriptions.

Instead, chances are that you mucked up your descriptions by saving them using something else from UTF-16 encoding (for instance ASCII, which supports only 256 characters total and lacks the support for characters used in Sweboz trait descriptions etc.).