Czech, Slovene and Portuguese relative constructions

In colloquial Czech, an invariable co is sometimes used instead of proper který, which must agree with its antecedent in gender, number and case.

Kniha, kterou jsme koupili, je červená.
Literally: The book (which) we (have) bought is red.
Kniha, co jsme ji koupili, je červená.
Literally: *The book what we it (have) bought is red. 

It turns out the structure of the second sentence is standard in Slovene, which usually only uses the cognate of který, kateri and variations, after prepositions:

Knjiga, ki jo smo kupili, je rdeča.
Literally: *The book which it we (have) bought is red.

After prepositions, the same construction coincides in both languages:

Počítač, se kterým pracuju, je nový.
Računalnik, s katerim delam, je nov.
The computer with which I work is new.

But in colloquial Czech, this is also possible, I don't know about Slovene:

Počítac, co pracuju s ním, je nový.
Literally: *The computer what I work with it is new. 

The funny thing is that in nonstandard Brazilian Portuguese there is the same thing:

O computador que eu trabalho com ele é novo, with the same meaning as above.