I am an Ecology and Conservation student at Lancaster University. In my first year I did 2 parts ecology and one part environmental science.
When I was selecting my "minor", we were given a handbook before we started which provided you with the potential options to take for your third part. For me, the options were restricted to a select few which were suggested as the best to complement you major choice. For an example, I was guided towards geography, environmental science and biology over something like film studies. However, I do know people who took subjects like Spanish, so Linguistics doesn't sound too out of the realm of possibility.
Unfortunately I cannot say for certainty what your options are. It may be worth contacting the department directly to get some clarification, but they will provide you with all your options in due course.
Hope this helps.
Jake (third year Ecology and Conservation student)