Does cuja refer here to língua or função? I thought it would refer to the word código as in English but then it would be cujo so I'm confused :P
Cuja here refers to língua. But pay attention: cujo(s)/cuja(a) agrees with the following word: esta é a mulher cujos filhos são professores.
Ah, it's all clear now, thanks Paulenrique!
Although it may be required in the Portuguese version, I think the definite article at the start of this English sentence would not, as it appears to be a general statement about any type of language.
What is the difference between língua and idioma?