普段「独り言を[言う](https://eikaiwa.dmm.com/uknow/questions/55091/)」は"to talk to oneself"と言います。
例 She is always talking to herself「彼女は[いつも](https://eikaiwa.dmm.com/uknow/questions/32890/)独り言を言っている」
"to soliloquize"は同じ意味ですが、かなり硬い表現です。名詞形は"soliloquy"です。
A soliloquy will help you learn a language by talking frequently.
Some people speak in monologues when thinking aloud.
Do not be afraid to use a monologue to talk to yourself.
独り言 monologue, speaking to oneself, soliloquy
独り言は、頻繁に話すことで言語を学ぶのに役立ちます。
A soliloquy will help you learn a language by talking frequently.
一部の人々は声を出して考えるときに独り言で話します。
Some people speak in monologues when thinking aloud.
独り言を使って自分と話すことを恐れないでください。
Do not be afraid to use a monologue to talk to yourself.