katakana - Does Okinawan have syllables Japanese doesn't?

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?

Answer

(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.

沖縄語の音韻講座（1）【ア行】《新沖縄文字へのいくつかの提案》

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。

沖縄語の場合は、声門破裂音かそうでないかによって、意味が変わってしまう単語があります。
「ʔうとぅ」：音、「’うとぅ」：夫
「ʔいん」：犬、「’いん」：縁
「ʔおーじ」：扇、「’おーじ」：王子

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).