However, I find the choice of languages limiting. I want to use
captions for languages - specifically for Chinese language learning/
teaching. The choices for Chinese are [as normal] simplified and
traditional characters. However, I need to use a romanization system
based on the western alphabet - such as pinyin for Mandarin, and the
Yale System, for Cantonese.

For example, Toronto written in traditional Chinese characters is 多倫多
and 多伦多 in simplified characters. No problem for folks proficient in
Chinese. Learners, though, need sth like "duōlúnduō" that shows the
pronunciation until they are able to read enough Chinese characters.

But there is no suitable name for this in your drop down box of
languages.

Perhaps others have similar needs.

Any chance of adding a "miscellaneous" category that we can customize
for our own purposes?