When exporting to DWG, fonts are not filled and clip masks are not shown.
Font mapping was suggested for the MicroStation filled fonts to a true type font, using text with a background set instead of using masking, and setting the update sequence for controlling where the image displayed (background, foreground, etc.)
https://communities.bentley.com/products/microstation/w/microstation__wiki/8817/fonts-in-microstation