When Windows is configured with certain locales (known to include Japanese, but likely others), the header text on all en-US (or presumably any Latin alphabet based) full installer pages uses a default system font that really looks quite rough. See attached screenshot, taken from bug 1515534 comment 14.

It might be tricky to detect this case, because presumably, for builds in the same locale as the system, the chosen font would be the correct one. But this looks so bad that it's worth at least investigating whether we can do anything.