My problem is that I can open xml files with one navigator but I think
that the encodigs of files are not correctly. The navigator opens the
files whith errors produced by the encoding. Can I put some kind of
encoding that was standard to open without errors and can open any
file?

Not quite clear what's the problem, but the encoding specified in the
XML declaration must match the actual encoding of your XML document. If
an application flags errors when opening the document chances are there
is a mismatch between the specified and the actual encoding.

In the absence of an explicit encoding, the encoding is assumed to be
UTF-8, and the document must be encoded in UTF-8.

    <?xml version="1.0" encoding="US-ASCII"?>       # ASCII
    <?xml version="1.0" encoding="ISO-8859-1"?>     # ISO-8859-1
    <?xml version="1.0"?>                           # UTF-8