IntelliLang: Cannot resolve symbol 'intellij'

This not an issue unless you want to actually use those annotations. In that case, you should add the annotations.jar library from %IDEA-CONFIG%/plugins/IntelliLang/lib to your project.

See also the documentation here:
http://www.jetbrains.net/confluence/display/CONTEST/IntelliLang#IntelliLang-UsingtheAnnotations

HTH,
Sascha