Can one fulfill the mitzvah of counting the Omer by counting in a language that only he/she understands? What if a few people understand? An entire goup?
From a psychological perspective, it would appear that what constitutes a language is where you have at least one or two people who think in that language.
For example, the rarest language in the world used to be a Celtic language that was only spoken when 2 elderly sisters met, it is obvious that is a language and could be used for sephiras ha'omer.
Also, there was a case of twins who grew up in an isolated area of Canada and who invented their own language. This is lichorah also a language which would allow them to count sephiras ha'omer (I.e why should they be excluded from counting sephiras ha'omer just because they made up their own language?).
On the other hand, if you can speak Elvish this probably does not qualify you to count sephiras ha'omer in Elvish because there is not one single person in the world who thinks in Elvish, so you have simply agreed with other people on a secret code way of speaking, which does not become a language.