(1) talk to oneself意为“自言自语”。

• He has a strange habit of talking to himself .
  他有自言自语的怪癖。

 (2) say to oneself意为“心想，想”，与think to oneself同义。

• “There must be something wrong”, he said to himself/thought to himself .
  他心想：“肯定出错了”。
• He thought to himself that he would do something to help her.
  他心想他将要做些什么来帮助她。

 (3) think aloud的意思是“自言自语”，也用作think out loud。

• Sorry, I wasn't talking to you, I was just thinking aloud .
  对不起，我没和你说话，我在自言自语呢。