My users are seeing (spammy) English ads on my website that's geared purely towards native speakers of another language many of whom know no English. I would like to restrict the language of AdSense ads to that language. Is it possible, and how?
According to Google itself
Language targeting: Our technology can also determine the primary language of a page. If your content is in a language supported by our program, AdSense will target ads in the appropriate language to your content. We may look at the language of the pages a user is currently viewing, or has recently viewed, to determine which ads to show. In this case, AdSense may target ads in the user's detected language rather than in the language of your content. Learn more about ad targeting by language.
In addition, we may look at the language of the pages a user is viewing or has recently viewed to determine which ads to show. This means that we may detect the language from either pages that the person had viewed in the past, or the page that they are currently viewing. In this case, AdSense may target ads in the user's detected language rather than in the language of your content.
I would look also at your page language declaration in the
<head>. Is it set correcty as the language of the document content?
Anyway, you should report a violation if you see spammy ads as Google suggest here https://support.google.com/adsense/answer/2631197?hl=en