It seems that consciousness can only be investigated through self-report, i.e. language/communication of some kind. Is it believed that consciousness could nonetheless exist without language?
Yes, it is assumed that non-human animals have varying degrees of consciousness - but this seems somewhat unverifiable without our capacity to ask them.
Conversely, has there ever been a human being to grow up without language for years and then learn a language sufficiently well to be questioned regarding their subjective experience prior to learning the language?