I have an Arduino project that has a sub-folder named "language" in the project folder.  One of the .ino files in the project references a file in the sub-folder; #include "language/en-GB.h"
 
I am getting the following error: fatal error: language/en-GB.h: No such file or directory.

The file does exist, and the Arduino IDE has no problems with this folder structure.  I have tried adding the language folder to both the include and library paths in project properties, but always get the same result.  Is there a step I am missing?  By the way, if I right click the file name in the IDE and choose "open document" from the context menu the file opens normally.