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Japan has a lot of topolects. Most of them are all classified under Japonic. These include Ryukyuan, Hachijō, Kyūshū and obviously eastern and western Japanese.
Can hiragana & katakana "spell" the sounds of all Japonic, etc. topolects?
Are there sounds and pronunciations outside of general hiragana & katakana abilities?
At least Okinawan has nonstandard kana to precisely represent their sounds. For example, Okinawan has two types of う ([u] and [ʔu]), whose difference is important for the local people to distinguish their native words.
Ainu also has special katakana, although Ainu may not be Japonic.
There is always a way to approximate their words only using standard kana, anyway.
To the best of my knowledge, in dialects in Honshu/Shikoku/Kyushu, no special kana is used. Of course there are regional varieties only describable with IPA (e.g., う is nearer to [u] than to [ɯ] in Kansai dialect) or allophones found only in some dialects (e.g., yotsugana and bidakuon), but they are not distinguishing features. (Bidakuon have special characters, but they are more like phonetic symbols to me.)
...50 years ago. Now they pronounce normal が行 [鼻濁音]{びだくおん}をきちんと発音する一般人は関東でも減ってますが、アナウンサー（特にNHKの）は現在でも正しく発音するように言われていると思うんですが。。。真面目なニュースのアナウンス聞いてたら、格助詞の「が」とかちゃんと鼻濁音で読まれてますよね。