Of course we aren't. That's the whole problem. We have different locales. That results in a header somewhere with the languages I understand in order of fluency

Of course we aren't. That's the whole problem. We have different locales. That results in a header somewhere with the languages I understand in order of fluency (which includes English, mind you), as per the specification. And the author of that web page decided to turn on an automatic translation tool to present its output instead of the original web page. That tool is particularly bad as it somehow decides that underware is similar enough to underwear that it should map the word to the word for underpants in my language. The rest of the page is a little better, but not by much. But the problem here isn't the quality of tool itself which results in particularly amusing choice of words but by the use of the tool itself. Don't do that. If the end user wants to read your page in a different language, they are perfectly capable of clicking that button in their web browser and deal with the outcome themselves. Just don't. I will not hunt down the language selection button on your badly translated web site and I will not change my web browser settings for your site alone. I will simply choose not to visit your web site, and I suspect many others will do the same.