Can ゐ/ヰ be combined with ゃゅょ/ャュョ?

Question

I'm writing a program which replaces kana characters with romaji, so that りょかん becomes ryokan etc. I thus need to handle cases where ゃゅょ (or ャュョ) combine with the preceding character.

My understanding is that they can combine with any -i kana character except い or イ. On this basis, ゐゃ/ゐゅ/ゐょ (or ヰャ/ヰュ/ヰョ) are valid combinations, being transliterated as wya, wyu, and wyo respectively.

I didn't find anything useful on jisho.org, but Wiktionary has a few examples:

• en.wiktionary.org has 永: よう (ゐゃう)
• ja.wiktionary.org has 洫: キョク (クヰョク)
• Various other pages mention ヰャゥ, クヰャウ, クヰャゥ, and クヰャク

However, I'm not sure if these would be applicable to modern Japanese - I get the impression that they may simply be historic spellings, and thus no longer relevant.

tl;dr: Would wya/wyu/wyo be considered be valid combinations (even if they're never actually used) in modern Japanese?

Answer 1

ゐ, ヰ, ゑ, and ヱ are not used in modern Japanese; they have been obsolete for almost 70 years. Most people do not even know how to type these characters with a keyboard. If you're not interested in the historical spellings of Japanese, you can safely ignore them altogether. (And serious support for historical Japanese is bound to be a huge task.)

Actually, these characters may appear in some recent proper nouns, for example ヱヴァンゲリヲン and よゐこ, just because they look peculiar and eye-catching. If you need to handle such cases, you can simply replace these characters with え or い, respectively.

You can type ゐ with wyi and ゑ with wye using most IMEs, and this was a part of JIS standard. But I think these are more like shortcuts rather than pronunciation-based transliterations.

I don't recall the exact combination of ヰャ/ヰュ/ヰョ used, even in the classic literature classes when I was a high school student. And I have no idea what wya, wyu, or wyo should produce—at least my ATOK gives nothing. Maybe they were used somewhere in the Japanese history, but I doubt it's worth supporting.

Answer 2

ゐゃ/ゐょ only appear in 合拗音 of archaic on'yomi system (ゐゅ isn't attested). Historically they were representing sounds like wya and wyo but they're very rare pronunciations in limited combinations ゐゃう (wyau), くゐゃう (kwyau), くゐゃく (kwyaku) and くゐょく (kwyoku) (maybe ゐょう (wyou) and ゐょく (wyoku) too, according to this paper).

The biggest problem is those spellings were (re-)discovered after abolition of historical orthography, that means, they have never been and will never be used outside historical study. I personally think it's not worth supporting but isn't a big deal to support too, as far as it won't break your other parts.

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PS
Things like くゐゃう should theoretically be written with small-size _ゐ, that corresponds to ゎ in くゎ. The lack of this letter I think explains how we don't use it.

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Further reference: 鎌倉時代における日本漢字音の位相的研究