If anyone arrives on this page looking for the same thing, I did a script to get what I desired: https://github.com/a455bcd9/wikilangtrends

Thanks for your answer. Too bad :(

And when I try to use the API with "all-wikipedia-projects" I get: https://wikimedia.org/api/rest_v1/metrics/pageviews/top-by-country/all-wikipedia-projects/all-access/2017/11

@leila No, as said in my initial message this is not enough. With this query only it's for instance impossible to quickly answer "What's the most used language in Morocco?" (French? English? Spanish? Arabic? Moroccan Arabic? Amazigh? etc.).

Actually there's maybe something simpler and as useful: instead of displaying the Wikipedias read by country one could easily calculate the % of views represented by one Wikipedia in a country among the views on all wikipedias in this same country.

@Aklapper Thanks a lot for reopening the task, I didn't know I could do it by myself. Thanks as well for changing the title. (I guess that's what you meant by "summary"?).

@Aklapper , sorry I've just read T188859 and I don't see how they're related. T188859 is about "the geographical origin of the contributors for a given wiki" whereas this request is about the total page views for each edition for a given country.

Thanks. FYI on Wikimedia Statistics, "New feature" directly points to Wikimedia Phabricator. It may be better to replace both the links "Report a bug" and "New feature" by https://www.mediawiki.org/wiki/How_to_report_a_bug