How to translate "once" and "every" in Japanese? 一度 or いつも

Question

[一度]{いちど(ひとたび)} means once, but [一遍]{いっぺん} also mean once in sentences like once I did something or once I am a something.

常に means always in sentences like I always am a something or I always do something

But idiomatically, Once bitten twice shy is translated as [羹]{あつもの}に[懲]{こ}りて[膾]{なます}を[吹]{ふ}く in Japanese.

So if I want to say Once a thief, always a thief, is this phrase grammatical 盗人一度, 常に盗人?

What if I want to say Once a X, always a X? and X is a noun/noun phrase?

Answer 1

I believe you are making the mistake of attempting to replicate an English pattern in Japanese.

As snailboat points out, the idiomatic equivalent is as follows:

泥棒はいつまでたっても泥棒。／三つ子の魂百まで。／性格を変えることはできない。

And if you make this search,

http://eow.alc.co.jp/search?q=Once+a+always+a

one finds that the nearest Japanese equivalent seems to be:

noun phrase はいつまでたっても noun phrase

If one uses the vocabulary you suggested, the nearest equivalent seems to be:

Once an actor, always an actor. 一度役者をやればやめられない。 Once an addict, always an addict. 一度中毒になるとやめられない。

Answer 2

For "Once a X, always a X", some suggestions would be 「Xはなおらず」 or 「XはXのまま」.