Please let me know if this is better to report this to the GitHub.

I was checking the handling of Extra fields Original Title and Medium by citations styles that are able to with some dummy citations.

By chance, I choose the University of Worcester - Harvard style and as far as I understand, the font between squared brackets should be in italic:
<macro name="original-title">
<text variable="original-title" font-style="italic" prefix="[" suffix="]"/>
</macro>
But this is not true for the third reference:

(One et al. 2024a, 2024b, 2024c, 2024d)

One, A. et al. (2024a) Paper 1.[Papier nº 1] Journal. [in French] 1 (1), 1–10.
One, A. et al. (2024b) Paper 2.[第2論文] Journal. [in Japanese] 1 (1), 11–20.
One, A. et al. (2024c) Paper 3.[論文] Journal. [in Japanese] 1 (1), 21–30.
One, A. et al. (2024d) Paper 4.[Papier] Journal. [in French] 1 (1), 31–40.

(I also join a screenshot to show I did not make a typo while transcribing the output:)
https://s3.amazonaws.com/zotero.org/images/forums/u2119014/1w813kylc8byujl0psse.png
It seems that the Japanese is only italicized when there is an ASCII character (second reference.) If I replace 2 by ２, it does not work. The same is true for >Università Pontificia Salesiana style.

Here are the Extra fields for each dummy citation:
Original Title: Papier nº 1
Medium: in French
Original Title: 第2論文
Medium: in Japanese
Original Title: 論文
Medium: in Japanese
Original Title: Papier
Medium: in French