There is no Arabic in the project, although in many cases there are words in other languages (Hawaiian, and another South Pacific language....) and diacritical marks such as a macron are there also.
I don't do much epub work - and when I do, InDesign is rarely involved - so I honestly don't know that much about why this is happening. However, I'm in the last stage of a project where it was important for me to have the Marshallese, Palauan, Pohnpeian, Chuukese, and Kosraean interactive PDFs language-tagged. So if it's necessary, I can show you how to add language tags for e.g. Māori to InDesign.
I also know that getting the language tags correct for multilingual epub export is important, and I have just checked out the preferences under File -> File Info, and the EPUB Export preferences, and the File Information dialog, and the epub export settings that you can find when you right-click on an object and select "Object Export Settings." I didn't find anything language-related in any of those places. That is in line with my assumption that the only place you can affect language settings is in paragraph and character styles. If you have Hawaiian or Māori or whatever in your epub, and you don't want to go throught the process of adding those tags to InDesign, those words should probably be marked with character styles having "[No Language]".
(Or alternately, you could tag all your Māori as another language Romanian, and then edit your CSS after export? But I'm going to tag @James Gifford—NitroPress in to your thread, as he's the forums regular I know to be expert in epub export from InDesign, and he always says that post-export editing shouldn't be necessary. Honestly I wouldn't know, as I am constantly elbow-deep in raw text formats manually editing Things That Experts Agree Oughtn't Be Edited Manually. I'm ready to be told by James that I'm doing it wrong, for what it's worth.)
So: do you consistently have styles applied throughout your document to all text, without overrides? Have you specified the language in each one? Do you maybe have a spurious Arabic tag appended somewhere in your template or base styles? Do you (kinda reaching, here) have a Middle East/North African install of InDesign for doing right-to-left work? Are you willing to share a sample epub that is flagging as "Arabic, English" for me to rip open, contra James' advice, to find where spurious "Arabic" bits may be hiding?
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