OK so this has been driving us crazy. We have an application built in ASP.NET 4.0 running on Windows Server 2012 and IIS8.
A few pages of our site are translated into multiple languages, notably Japanese and Chinese are the problematic ones.
If we put the application pool to integrated mode - some characters do not display correctly. We're greeted with little question marks.
If we put the application pool in classic mode, all the characters display correctly. Unfortunately this isn't a long-term option for us since it breaks other functionality on the site.
Fun thing - if we change the 'Enable 32-bit applications' setting in Application Pools -> Advanced Settings the pages still display bogus characters however they display different characters incorrectly.
Originally we suspected a bogus character in the page or an encoding problem - but we've quadruple checked everything and verified all the content is utf-8. Switching the application pool to 32-bit and seeing different characters display incorrectly is leading me to think perhaps something is wrong in IIS.
Thanks in advance for any help/insight/experience.