We do talk about "switching careers". But a "switcher" is just someone who switches, just as a "dancer" is someone who dances. It can be used for anything, not just careers. If you want to use the term in conversation, then at first you should say "career switcher" and thereafter you can just say "switcher".

There is a book called Switchers discussing this subject, but it's not something that regular people usually say by itself.

We wouldn't really have a word or standard phrase in the US. Most commonly we would just say 'a career change,' 'changed careers,' 'started a new career,' 'changed professions,' etc. It depends on what connotation you would want; the above options have a neutral or maybe a positive connotation. 'Career switchers' or 'job switchers,' like Glenn offered could work, but they aren't very standard and I would perceive them as having a more negative connotation, i.e. someone who doesn't have a stable career and changes jobs frequently. In the US, changing careers may often have a positive connotation as it suggests you changed for the better, found a more fulfilling career, got more education/training, learned a new skill, etc. Sometimes you'll find office workers romanticizing a career change, for example, like in Office Space.