Languages on windows

I have the japanese language pack installed on my computer and yet error messages / task bar still comes up as ???? and random signs.

What's up with that?

If you mean the "random" symbols appear when trying to run a Japanese program (say, Fate/Stay Night or anything else that requires AppLocale), then you didn't configure the default code page.
Control Panel/Regional and Language Options/Advanced tab. Then in the drop box select "Japanese".