I wonder what bias you find in my historical account. That until 1931, Basque was considered the origin of Spanish? Since it is widely claimed that Basque is a remnant of Iberian dialects, it could have some truth in it. Or is it that from that time on, and in accordance with ultra-nationalist political movements in Europe (nazis, facists, and so on), some people like Sabino Arana, tried to discover the essence of the Basque Volk in its (invented) language? I have honestly tried to give you historical facts, but if you know better, I'd like to hear your unbiased account.
My position on your list above,
1. Communication.
Yes, language is a convenient tool for that
2. Identity.
Yes, language is the way each person has to formalise her/his environment. For me, there is only MAÑANA, MEDIODÍA, TARDE and NOCHE. For you there is MORNING, NOON, AFTERNOON, EVENING, NIGHT. For me there are LENGUAJE, LENGUA and IDIOMA, whereas for you there is only LANGUAGE. In that sense, I agree.
In the sense that language could be considered the perceivable equivalent of race or territory, I prefer to be careful. I lived for 40 years under a fascist dictator, and any trace of nationalism, patriotism, etc, makes me a bit nervous. This is perhaps the reason of your cavalier indictment of my biased account, come to think of it. If it is, then yes, I am not nationalist, nor patriotic in any sense, as I am not religious. I feel human, period.
3. Linguistic data.
OK, if you like archaeology, I understand. Pity that present day Basque is a modern contraption invented last century, but ...oh well, who cares? BTW, when I was studying in Edinburgh, aeons ago, some of the linguistics department staff invented a new language, NOVISH, to illustrate different linguistic problematic possibilities. This was really an interesting language for a linguist, with no hint of romanticism, nationalism, racism or any other more or less disgusting -ism attached to it.
4. History, literature, knowledge, etc., within the language (like names of local species of plants or animals).
Basque did not have any literature until after 1931. Traditional Church had put in some Basque dialects (with a completely wild orthography, for it had never been written before) sermons, bible texts, and so on. The whole of the Basque literature that we now have dates from after 1931.
Of course, I am biased. But telling the truth sometimes is, I'm afraid.
(On the other hand, I would never indulge in that biased account with Catalan. It has always been a widely used language).