There are at least two possibilities. The first one that comes to mind is a graphics card issue. See Why am I getting weird graphics issues?. I think it might also be possible that there's a problem with the font installed on the problem machine. I wouldn't know how to go about fixing that, but I'm sure someone else will.
As far as applying a dimension font change to all drawings, yes, you can. It's easy enough to make the change to a new drawing, then save as drawing template. I assume you already know how to do that. If not, I'll be happy to elaborate. After that, all new drawings using this template will use the new setting.
It's also possible to save the drafting standard from a document with the correct font, and use it to update existing drawings. See Why aren't the changes I made at Tools > Options > Document Properties saved when I start a new Part? for more information on both. There's probably a process to automatically update existing drawings without opening them and doing it individually, but I'm not familiar with the details. I'm sure someone else will be able to help if you need to do that.