You're not alone with this issue.
Anyone would know how to fix a single letter in Font?-fontsubstitute-segoe-dotum.png
gives me the following results
Anyone would know how to fix a single letter in Font?-dotum-font.png
Anyone would know how to fix a single letter in Font?-folder-path.png
Anyone would know how to fix a single letter in Font?-systray-clock.png
I haven't figured out yet how to replace the W using Fontforge.
If i find a solution, I'll describe it.