Like many languages, the Chinese languages have their own special names for some famous places. For everywhere else, there’s a standard transcription table mapping phonetic sounds to characters. Apparently each Chinese-speaking country has its own standard.
What’s tricky about San Francisco is that Hong Kong has largely abandoned the traditional name in favor of a phonetic transcription, but the PRC and ROC have not. So here in the San Francisco Bay Area, you can see both names on signs, on TV, etc. (The U.S. government doesn’t regulate the English language, let alone Chinese.)
You might want to check whether the name:zh tags in your country can be found in a dictionary, adhere to a particular language standard, or are just one mapper’s whim. Sometimes language enthusiasts strive for language coverage a little too zealously. That said, I have noticed that “eyeballing” a phonetic transcription is common practice among South Asian languages, both in OSM and elsewhere. Whether it’s right or wrong is not really for me to judge, since every language does things so differently in reality.