Meaning of が and おく in 言っておくが? [duplicate]

Question

言っておくが、私に怒っても始まらないよ。= I'm telling you it will do you no good to be angry at me.

Does が mean 'but' in the sentence? Does おく mean 'in advance' in the sentence?

If YES, what lead to the translation above?

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Note:

A related question 言っておくと

Answer 1

You are more or less right. て-form + おく means to do X in advanced for the benefit of the future and X-Phaseが、Y-Phrase is usually X-Phrase, but Y-Phrase.

However, after spending a lot of time translating from Japanese to English one major point of advice I can give is don't get too hung up on the directness/one-to-one match of a translation. There are just some things that don't translate directly well and will require the translator to take some freedom in making the translation sound and feel good for the audience

Lets break down the sentence you posted and translate it to see this in action

The first and main part of your question:

言っておくが =>

言って + おく + が
To say + to do for the future's benefit + but

So by assuming I is the speaker, we can "Englishify" this to:

言っておくが
I'm telling you (for your future's sake but)...

Now lets take the Y-Phrase part and break it down:

私に怒っても始まらないよ =>

私に + 怒っても + 始まらない + よ
I to + to (even) be mad + no use + (ending)

After "Englishifying" it:

私に怒っても始まらないよ
There is no use in being mad at me.

Putting it all together we get:

言っておくが、私に怒っても始まらないよ
I'm telling you (for your future's sake but)...　There is no use in being mad at me.

Cleaned up final version:

I'm telling you... There is no use in being mad at me.

Now lets compare with the translation you provided:

Breakdown Version:
I'm telling you... There is no use in being mad at me.

Provided Version:
I'm telling you it will do you no good to be angry at me.

As you can see both English versions have the same meaning at the end of the day. BUT where the important point comes in is that the translator had the freedom to get to this final English version. Where it feels good and natural to the target audience, English speakers, in this case.

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In response to raruna's first comment:

When you say "here" I'm going to assume you are talking directly about the 言っておくが part and its relation to the English translation.

With this and the English translation you posted and even the one I did kept in mind, I want to say "No". Translating が to But doesn't necessarily make sense here. Here が is more of a unsaid filler word or pause when translated to English.

This goes back the point I cannot stress enough, which is you should not try to do direct translations/one to one word matches or try to force what I will call "textbook examples" when translating.

The X-Phraseが、Y-Phrase meaning X-Phrase, but Y-Phrase pattern is a easy to understand textbook example for beginner Japanese learners that is used.

And this works 95% of the time when translating from Japanese to English. But in the example you posted we can see this starts to fall apart when we are trying to make the English translation feel natural.

Keeping all of the implied meaning, everything in parenthesis, in the translation version I did we have

I'm telling you for your future's sake but... There is no use in being mad at me.

From a native English speaker's perspective this just sounds weird and requires clean up to make it feel more natural, which is a essential part of translating to a different language.