non-standard language tag in OSM

Currently, there are the following non-standard language tags in use in OSM for Chinese, Japanese and Korean:
ja_rm, ja_kana, zh_pinyin, zh_zhuyin, ko_hanja
BCP47-compliant expression for these tags should be:
ja-Latn, ja-Hira, zh-Latn, zh-Bopo, ko-Hani. And then there’s also ko-Kore which can be used to represent Hangul-Hanja mixed script for Korean but it is basically not being used.
The two BCP47-compilant Japanese tags have gained some usage in tens of thousands location but there’re still tens of thousand location using those old tags, is there a way to and should an action being performed to change all of them at once?
And then what should be done about those Korean/Chinese language tags?
And for non-Mandarin-speaking-Chinese-area like the two SARs, should the context of “zh-Latn” be reserved for local Chinese languages while Mandarin pinyin use cmn-Latn insetad?

Is there any need or advantage changing these? (Honost question, it’s the first time I hear of BCP47)

As for your last question: If we change zh-pinyin to cmn-Latn. Don’t we have to change all those zh to cmn and others (which in each case?), too?

I’d suggest contacting the people who’ve added these tags and asking them (not in an accusatory way) way they added those tags as opposed to others. It may be they made a genuine mistake, or added them ages ago and agree that they should be changed.

I’d also suggest asking this in a more active international forum than this one - find out where the tags that you’re interested in are and find the forum that mappers there mostly use. Also, the Q&A section of this forum gets relatively little traffic compared to some of the international English-language mailing lists.

So hopefully other software can understand those codes even without particular adjustment based on info on OSM wiki.
For instance, only software that are developed with OSM in mind and referred to the wiki would know what “zh_zhuyin”, “zh_pinyin”, or"ja_rm" are. However, if the standard is used then programs would understand they are Chinese in bopomofo zhuyin, or Chinese/Japanese that are spelled using latin alphabet version of those languages (as in the romanized versions)
It is useful in places like browser display (like romanized tag can use latin character font to display instead of Ideographic character fonts), communicate with external database (for instance other databases like wikidata use BCP47 for language tags), and such.

Not really, because, 1. other than in the two SARs (Hong Kong and Macau), it is generally okay to use zh to imply cmn as when one say Chinese in most places around the world one would immediately understand that is about Mandarin, but within the two SARs there are exception, and then 2. Even when “Chinese” does not mean “Mandarin”, in most of the time when written in Chinese characters for proper noun, they would be the same [And even when they are difference, since Standard Chinese is the standardized Chinese writing form in both territories, the “zh” tag will still be used to describe the cmn-, as in Mandarin(Standard Chinese)- based writing, with additional yue language tag for Cantonese based form in characters. However the romanization will be different, and Cantonese romanization is being used to romanize most place names in both territories.
But then there’s also another option to just put Cantonese romanization in yue-Latn while keeping Pinyin in zh-Latn as long as people can agree to that.

[quote=SomeoneElse]I’d suggest contacting the people who’ve added these tags and asking them (not in an accusatory way) way they added those tags as opposed to others. It may be they made a genuine mistake, or added them ages ago and agree that they should be changed.

I’d also suggest asking this in a more active international forum than this one - find out where the tags that you’re interested in are and find the forum that mappers there mostly use. Also, the Q&A section of this forum gets relatively little traffic compared to some of the international English-language mailing lists.[/quote]
hum good idea. But a problem to me is that now I don’t even know where people living in my city talk about OSM online, that would need some extensive searching…

I can tell you why I added those. They have been well documented in the wiki for years.

You can look up the changeset in which those tags were added and make a comment on those. Or use the OSM message system to send the authors of those changesets a direct message.

or use http://resultmaps.neis-one.org/oooc to find mappers around you.

Actually #Issues section of the Multilingual names page have also described BCP47 with relative details.