[salamandersauce]

Japanese has a couple syllabary to fall back on. If you don't know the Kanji for a word you can use the hiragana/katakana version which is pretty much 1:1 with how it sounds. If you use too much hiragana can become a bit unpleasant to read though.

[Retric]

What’s the Chinese equivalent? As I understand they have multiple distinct spoken languages sharing the same writing system.

[salamandersauce]

I don't know any Chinese really so I can't comment too much. Taiwan has a syallbary called Bopomofo and PRC has Pinyin but I think those are only really ever used for typing/teaching. Parts of Chinese characters do have a phonetic component typically and from what I've heard this maps better onto Chinese than Japanese where possible sound could have very little or nothing to do with the phonetic component. So you could maybe write another character with that component maybe?

[dwohnitmok]

> they have multiple distinct spoken languages sharing the same writing system

It's... complicated. If you sort of squint the writing system is maybe the same in the sense that across different Chinese varieties cognates are almost always written the same way (e.g. Cantonese and Mandarin). But a lot of non-prestige Chinese varieties don't really have a standardized writing systems (although a very interesting phenomenon is that speakers can generally tell you when a given word has an associated character(s) they could write down for you and when they can't think of one). So usually when a writer of a non-prestige Chinese variety writes she/he is writing in Mandarin, not in the variety itself.

Nonetheless, there have e.g. been historical Chinese novels written in non-prestige varieties (e.g. in Min or Wu) so in that sense yes the same writing system can and has been used, but different authors might use different characters depending on how they understand the relationship of certain words to the prestige variety.

Even the different languages part is complicated. https://news.ycombinator.com/item?id=16844074

As for what phonetic "spelling" out happens in Chinese, usually a loan character is used (e.g. if live transcribing something where the transcriber hears some unfamiliar words, the usual solution is to write down characters with the same sound and mention that this is purely a sound loan in parentheses).