How to make a menu to switch subdomains of a wordpress site?

Question

PHP

There is a site xxx.ru
and it has several subdomains: 1.xxx.ru, 2.xxx.ru, etc.
How can we make functionality that will allow us to switch between them? Preferably something in the form of a drop-down list. maybe there is a plugin for this?

Answer 1

And what does the mechanism of arbitrary links of the standard menu provided by the engine not suit?

Answer 2

If you do it <select>with nested links, is it really a collective farm?