What brand and model router is it, and what version of the router firmware is it running?

Have you been able to look at the "Page Source" of the page it's offering to translate? I mean, yes, I believe you that the page is written in English when viewing normally, but does the raw source code show anything that Chrome might be flagging as translatable?

I'm not certain, but I'm guessing that all that Chrome does is to scan the page and see if there's anything in Chinese. You see only English there, but maybe there's something in Chinese, perhaps something not visible, or at least, not easily visible. Such as something printed in white-on-white text (visible only if you Select All), or something in a hidden DIV, or perhaps an ALT tag that didn't get localized.

I'm also assuming that this only started happening recently, rather than something that's been ongoing for a long time, correct? If so, then my guess is that one of two things must have changed: Chrome changed its translator behavior in a recent update to make it more sensitive, or, the router firmware got updated to include a regression in its localization as I described above.