Make getLanguage return client-set language

Previously, getLanguage returned language set on the TTS service side.
In most cases client wants to receive value that was set on the Client side
(value that was set by last call to the setLanguage). That's true, for
example, for android settings app.

This is not an issue if there's only one client, or when all clients use the same
language. In that cases, service and client languages are in sync.

But if there are multiple clients using different languages, getLanguage might
return values that were not set by the client - and that's not what most of clients expect
to happen.

Change-Id: I5fd8313725e677c20fb2a84a087fc7555897bd30