I hope I won't be considered presumptuous if I offer some advice.

如果我提出点忠告，希望不会显得冒昧。

May I make so bold, sir, as to suggest that you try the grilled fish?

先生，我冒昧地建议您嚐嚐烤鱼。

Or the writer may, riskily, ask the questioners what is real, anyway?

有的作家或许会冒昧地反问提问题的：究竟什么是真实？

I took the liberty of borrowing your dictionary while you were absent.

你不在时我冒昧借用了你的词典。

I ventured to write to her.

我冒昧给她写信。

I venture to say that....

恕我冒昧地说...。

Excuse my -ties.

请原谅我的冒昧。