SXB,
Agreed, the ECHR is a public law instrument (indeed the UK Human Rights Act can only be used as a cause of action against public bodies) but it imparts rights, which are enforceable against anyone seekingto infringe them. That is, a right to privacy of correspondence must be observed by both government (can't open my mail) and, say, an employer (can't open mail addressed to me without a legal, justifiable reason - which may include 'business purposes').
So my point is that right to expression - which in the first paragraph of Art.10 carries no qualification, unlike para.2 - is a general right.
Whether the right to freedom of expression extends to freedom to always use a language one chooses (rather than the content of what one says) has not, I think, been tested.