Hi!
I have the solution, it came with the extra languages that the site is in now 🙂
For the calendar starting with Sunday, use airbnb.COM
For the calendar starting with Monday, use airbnb.CO.UK or any European country ending (.de, .si, .cz...)
Check the ending of your country, if the site is available in your language too.
You can also still change the language and currency in the dropdown menu of your profile, but sometimes it still doesn't change the country ending in URL.
Hope this works for you as it works for me!
P.S.: I did notice that Promotions tag button does not show the same in different country pages (eg. it shows on .com, but not on .co.uk, or vice versa), so make sure to change the ending from time to time if you want to set a promotion tag, but don't have the option 🙂