The View | Context Info feature is supported for custom languages since IntelliJ IDEA 10.5. In order for it to work, you need to have a structure view implementation based on a
TreeBasedStructureViewBuilder, and additionally to provide an implementation of
DeclarationRangeHandler for your language and to register it in the
declarationRangeHandler extension point.
Spellchecking can be provided via EP
SpellcheckingStrategy) where you can return Tokenizer to use, possibly depending on the passed in
EMPTY_TOKENIZER for no spellchecking).
Check out a step-by-step tutorial how to define custom language support on example of ".properties" files: http://confluence.jetbrains.com/display/IntelliJIDEA/Custom+Language+Support