My google maps account is in Spanish, so when I open google.maps.com I see spanish names.
travellerspoint.com's intefeface - in Engish
I log in form Argentina and have IP from Buenos Aires.
But the google map inside the website is in Russian.
I have russian language at my PC, but changed Region to Argentina.
What else should I do to change the language of the map?
Check your browser's language settings. I'm pretty sure that's the one that is used by Google to decide the map language.
I changed my Chrome language to English, deleted all the cookies, re-logged in and the map is still in Russian
Just to confirm - you would need to go to this settings page in Chrome:
Then ensure that Spanish is the top language (or whichever language you prefer) and maybe remove Russian altogether.
Then hit refresh on the map page. Just tested changing these languages and that worked every time.