According to that Google page:

although English is still the most popular online language, it still only accounts for one in four users

Well, I have translated most of my websites in many languages well over 10 years ago. Whilst I agree with that statement, I must also point out that 80% of my income comes from websites in English. I do have sites in Chinese (world's no 1 language)... but their income is almost nil.

Spanish is also far behind English in terms of income, and another interesting example: although the majority of Spanish speakers are in South America, and only a minority in Spain, it's Spain which is the biggest earner in Spanish.

The quantity of native speakers in a given language does not correspond to the amount of money they can generate.

it’s probably not necessary in Holland where 87% of people speak English. But in Poland, 95% of people prefer online content in their native language.

That does correspond to my experience. Actually here is my language ranking by income: 1) English; 2) Spanish (in Spain); 3) Polish; 4) French.

Thank you SilverSpirit, that's valuable information, and will greatly help those that are looking to new language markets.