I know Okinawan is usually (nowadays) written in katakana. However, katakana only has a limited number of different syllables, fewer than can be produced in, say, English (e.g. th). Does Okinawan have any syllables that don't fit in standard katakana? If so, how are they written?
(Disclaimer: my knowledge on phonology and Okinawan is very limited)
The glottal stop (/ʔ/) is a distinguishing feature in most Okinawan dialects. /ʔa/ and /a/ are different sounds in most Okinawan dialects, although they are both ア in katakana. The /ʔ/ sound is important in no dialects found in mainland (non-Okinawa) Japan.
沖縄語の「あ・い・う・え・お」には声門破裂音とそうではないのと2通りあるということは、10ヶ月前の記事で書きました。 (snip) この[ʔ]の有無が「弁別的な機能を果たしている」ということが、沖縄語の特色なのだということも書きました。
To distinguish in writing:
- Professional researchers seem to simply stick to IPA notations.
- 沖縄語辞典 issued by 国立国語研究所 uses
'あfor /a/ and
ʔあfor /ʔa/, and so on. This rule is also used in the article above.
- 船津好明 invented some new hiragana characters (!) to represent vowels without glottal stops, which are also briefly introduced in the article above.
There are also some sounds which are no longer used in modern (mainland) Japanese, but the writing system using kana doesn't seem to be very standardized. 船津 uses these new hiragana, and other groups use various combinations of existing kana to represent such sounds. See this chart. This article by 船津 (PDF, in Japanese) compares three proposed orthography systems using kana (including his own system).
Yes, many sounds from Okinawan languages do not fit kana, but everyone sort of makes do with hiragana, katakana and kanji.
On that note, it is only common to write Ryukyu words in katakana when the main sentence is Japanese and mainlanders are going to read it -- in particular if mainland Japanese are the ones doing the writing. Locally we often don't think about the difference, sort of like how people in Texas often mix Spanish in with their English without bothering to italicize it.
Here are some pictures I took from one of my kid's picture books written in ウチナー口. You'll notice that hiragana is used normally, with katakana only being the onomatopoeia type words. Very often we use small character sizes to represent certain characteristics of pronunciation, but this is not an easy thing to do when typing (like here) because I don't know how to input, for example, a small わ (but a small い like ぃ is normal). Also notice that there is a word starting with ん here, which isn't entirely accurate to the way the word really sounds, but again -- people mostly just make do with kana.
You'll notice that the story pages have an inset in Japanese in addition to the main text in ウチナー口.
EDIT: After writing this answer the book was on the table and one of my kids read the title. I then realized that 「えんそうくゎぃ」 is a good example of a sound everyone knows to say correctly but we don't actually write with the correct letter. The first character, え should really be a (now very rarely used) ゑ which is one of the now "missing" two letters in the やゆよ line of kana, this one corresponding to a sound like "ye". In daily life we only ever see this character in katakana for the beer brand ヱビス. This letter and sound is not specific to Ryukyu languages, it has mostly fallen out of use in most of Japanese as well (ヱビス is produced by Sapporo -- about as far from Okinawa as possible).
As a weird side note, older Okinawans often pronounce "English"/「えいご」 as 「ゑいご」 out of habit.
Seek, and ye shall find. :)
This is a decent English-language description: