It's not possible to disable a certain language. What you can do is choose "Don't like" or "Don't play this again" for any song or artist you don't like. That way you'll be presented with better recommendations. Here's some more info about how the Discovery Weekly playlist works.
Hope it helps! Let us know if you have further questions.
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@Guido Lies, I have been doing that and selecting that "I do not like" and "Do not play songs like this" option to every foreign language song that keeps popping up in my playlist for the past 6 months and I'm still getting them.