Re: By way of example.

Just focus on this part, don't assume anyone trying to log in to anything, 
it's just a straightforward example of a resource which has representations 
in multiple languages so that Spanish-preferring clients see the Spanish 
version and English-preferring clients see the English version of what 
appears to be the same resource?

http://example.com/instructions?hl=en
http://example.com/instructions?hl=es

So long as each URI (I prefer using en.example.com and es.example.com 
instead of /path for this) is providing instructions *for the same thing* 
we have no collision.

But some websites would use a format like this, which is RPC/wrong:

http://example.com/instructions?id=fixing-a-lawnmower
http://example.com/instructions?id=making-a-martini

Clearly, two resources feeding through the same URI, /instructions, and 
leaving absolutely no idea of what might happen if /instructions is 
dereferenced by itself with no parameter or query.

-EJB