How to adjust the lexer used by pygments highlighting

The highlighting via pygments actually works quite fine in general, but 
in some cases it uses the wrong lexer and then has bad results.

It _seems_ that pygments' "filename (extension) based" language lookup 
is not used, because tested files using `pygmentize` are always well 
colored, the ones in GDB sometimes use the wrong lexer.

Question: How can we adjust the lexer used by pygments syntax 
higlighting in GDB for a given file?

Is it possible to setup a filename extension-based selection when GDB 
does not know of the language ("set language " _seems_ to have no effect 
on highlighting, but that would only work if the language is known to 
GDB)? If not can the "normal" extension list [1] be added to GDB or the 
decision which lexer to be used passed on to pygments?

Thank you for any insights,
Simon

[1]: https://pygments.org/languages/