See https://lrc.wikipedia.org/w/index.php?diff=135881 for an example (with a left-to-right language as the user language)
When DifferenceEngine/Article (this applies to both) shows the difference-missing-revision message, it will output it directly through OutputPage::addHTML. This causes it to end up in the mw-content-text div, which has the lang and dir attributes set to the values matching the content language of the wiki. This means that any content within that div will inherit these unless overridden. Given that interface messages are in the user language, this causes issues when those two differ, which is especially noticeable if the user language and the content language have a different directionality.