Blissymbols

I presume conlangs ignore this by design as fixed language. They are formed and mostly governed by rules, but the anthropological component of language never makes it into the design because there is no timeline of evolving usage.

And again, presuming here, but the outcome is a language that fails to adapt to the culture(s) that depends on it, and thereby becomes useless. Language, as we know it, evolved over an expansive period of time, from the first association of sounds to objects, now all the way to complex written grammar that includes some half-dozen tenses, some gendered, singulars/plurals, etc. We can describe things with written language that are otherwise indescribable with physical or spoken language, like the Portuguese saudade (a physical and emotional state of intense, fixated longing for someone or something that is absent, or which existed previously in a different state).

Languages in the Loglan family, notably Lojban, have an explicit audio-visual isomorphism which maps phonemes to/from letters. In theory, this should allow people to learn to read and write long after they have learned how to listen and speak; in practice, it seems to lead to many alternative orthographies and a fragmentation of readability.

Most conlangs aren't like Blisssymbols -- they have normal words that are made out of roots that can be understood either within the context of the language, or as in the case of languages like Esperanto and Interlingua, use roots from other languages so that word meanings can be guessed from knowledge of other languages.

For much of European history, Latin acted as a common written language, and Italian, Spanish, French were vulgar Latin with different influences (this is probably a simplification)

I'm a native Spanish speaker. I can understand written French, Portuguese and Italian with a little effort. Speech is a different story. Italian is the closest phonetically.

This is exactly how Arabic works today. It's a huge impediment, not a benefit.

Arthur Waley was one of the greatest translators of classical Chinese and Japanese poems. Supposedly he never learned to speak modern Mandarin or Japanese.

You are not the first one who has asked that question. In case you can't watch videos right now, the short answer is "you can guess, but don't expect it to be exactly correct".

https://www.youtube.com/watch?v=-E6vHCT0wpw

https://www.youtube.com/watch?v=rzJqXd-1dEU

This sort of thing happens in a lot of languages though. Your average Italian can comprehend a decent amount of French text without being able to keep up in conversation, or even speak the language. Same with Dutch and German.

I am not Japanese but have spent enough years studying the Japanese language to develop some amount of literacy, so I can give some insight (but take this with a grain of salt, it's not my native language). I can read enough Chinese to understand the basic topic of some sentences, but Chinese grammar is completely unrelated to Japanese grammar and Chinese characters used for grammatical constructs (e.g. Chinese particles, aspect, etc.) are not really used in Japanese (or are used in totally different ways). Nouns are easiest, adjectives and verbs are sometimes sensible, but beyond that it is hard.

My Chinese and Japanese friends tell me that when they have traveled to Japan or China they have used a pen and paper to communicate basic things.

One challenge is that character simplification is somewhat out of sync between communist China (Taiwan and Hong Kong rejected simplification) and Japan, so sometimes a character will be hard to understand even though I know its original or differently simplified form.

A final point: I can read enough Chinese characters to be amused when I see a Chinese takeout restaurant with an English name that has no relationship to its Chinese name.

A good place to start could be Japanese grammar which relies heavily on relational markers (so-called "particles"). It would also be appropriate since Emoji originate in Japan.

For example, to express something like "I went to the grocery store yesterday", the corresponding Japanese sentence would be structured like this: "I <topic-marker> grocery store <destination-marker> yesterday <time-marker> go-<past-tense-suffix>".