I added an artist tag by using the name from the description and decoding it into it's Unicode entities (and replaced the % with & but maybe _ would be better).
=> ドロマメ -> %u30C9%u30ED%u30DE%u30E1 -> u_30C9_u30ED_u30DE_u30E1 -> u_30C930ED30DE30E1
Basically every artist tag matching this regex ^_u([0-9A-F]{4})+$ would be a Unicode one.

Is this an acceptable strategy to give artists with non-ASCII handles a tag?

see forum discussion

EDIT: _u.... -> _u.... ("_" can't be the first character in any tag.)

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EDIT2: as discussed in the forum topic (linked above) this is not a useful solution to the problem. Thus I replaced the decoded artist tag with a romanized one.