One of the reasons is because people use the AdSense English language community and write in their own language. For the majority of languages, Google Translate is your friend! You can type your question into Google Translate and ask it to be translated to English. Then post the English version when asking for help.
You'll probably get help (or at least an answer) faster than if you post in a non-English language in the English help group.
Some of the forum PEs (that stands for Product Expert which is what Google call us these days) might answer questions posted in other languages, but not all devices have on-page translation, so a lot of non-English questions might go unanswered. I try to answer as many of them as I can, but not all languages translate into questions that make sense, and if we can't figure out what help the person is asking for, we can't answer the question.