Google recommends use sub-domains or query path part as definition of current language, so URL will look like https://lang.example.com or https://example.com/lang/.
And there are reasons why I think these recommendations are bad:
1) When user will share link, language will be hardcoded.It's not obvious when your main language is English, but if user is from Italy, for example, and wants to share some URL from Wikipedia in his favorite social network, all users, from all countries, will open that page in foreign language and will be forced to search where is the language-switching button on that site. Try to find that button on Google Webmaster Tools site.
2) It's bad for semantic web.Water is a water. In France, Italy, Germany and even in Soviet Russia, water is H2O. So by URL wiki.org/water (it's example) I suppose to find something about water. Will de.wiki.org/water or wiki.org/fr/water point to different resource, not water? If not - why different URL?
3) Language is just an option of content representation, same as background color.Main thing is the meaning of that content, not color or language or rounded borders. So use URL parameters, which you use for other options. It's not intuitive to use us.example.com/api/ and in.example.com/api/ - is it different APIs? Will their responses be different only in language or in some other things also? Time in response will be in PDT or in IST?
But it's Google recommendations, source of traffic...
Of course it's enough reason to follow these recommendations if you want to optimize your site as much as possible for free visitors from search engines. But I'm sure that sites should be for humans, not for search engines. And I hope some engineers from Google will read this (or similar) article and will change their recommendations.