If you a) create a text index with the default language set to an RLP-only language and b) forget to specify the RLP command-line option the next time you start mongod, you'll see an error message like this:

[initandlisten] Assertion failure swl.getStatus().isOK() src/mongo/db/fts/fts_spec.cpp 95
...
[initandlisten] exception in initAndListen: 0 assertion src/mongo/db/fts/fts_spec.cpp:95, terminating

It'd be more user-friendly to mention that the error is related to text index languages.