My understanding is that name=* and name:xx=* follow actual use by the language/locale population, not necessarily official use by the White House or other authorities.

@JeroenHoek I understood when I replied to you earlier about this.

>https://taginfo.openstreetmap.org/keys/name%3Aja-Kana

Thank you for this

There is no "should" or prescription, but acknowledgement of prevalence in American English (as opposed to British English, already acknowledged in tags) regardless

ja-Kana is BCP 47, unlike ja_kana, but despite some obsolete kana that make hira⇔kata not quite perfect, it should be unnecessary and I'll probably leave it out going forward