On the new version of MediaWiki, titles' fonts became sans-serif (instead of serif) for Hebrew, Japanese and Korean (see gerrit 217707 and the bug I wrote yesterday).

There is a little problem: Only Hebrew letters should be sans-serif. English letters should remain serif.

On Hebrew projects, when the title is in English (or contains some Hebrew and some English), the whole heading is sans-serif while the English text should be serif.

Here's a screenshot from hewiki. The title is sans-serif, but the word "YouTube" should be serif (the quotation marks should still be sans-serif):