Kdjykuj

In German, there's an idiom that goes like "Nagel mich nicht darauf fest" (literally, "don't nail me down on that!") usually followed my some kind of information that is given without complete assurance or guarantee that it is correct.

Now I'm wondering what would be the correct way of saying this in English. Is it "don't pin me down on that!"? Or something else?

"Don't hold me to that!"

to hold Vocabulary.com

• keep in a certain state, position, or activity


• maintain (a theory, thoughts, or feelings)

And your suggestion is nice too:

• 
  

  'Don't pin me down on this'

  
  

and does not carry negative connotations.

I would suggest don't quote me on this as the phrase you seek. The literal meaning of course, is to ask that responsibility for a statement not be ascribed to the person making it, such as an insider leaking private information to a journalist. It is a request that the statement be paraphrased, perhaps, but particularly that the name of the person making it not be indicated.

From there, don't quote me has taken on a sense of I believe what I am saying is true, but I may be inaccurate in particular details or I am presenting gossip or conjecture as truth, but I do not have factual information to support it, and from there it has perhaps become an even more generic mechanism for distancing a speaker from the statement. It is often used jokingly in this way, to make a humorous impression, draw an outrageous analogy, make an insulting comment, and so on but quickly indicate to the reader or listener that the speaker is not making a serious argument.

Literal sense of "please do not ascribe a quote to me":

"Holy shit!" exclaimed one Republican on the Armed Services Committee when a reporter shared the news about Mattis. "Don’t quote me on that." (The Hill)

Sense of I am making a statement but understand my information is incomplete or inaccurate:

The West Virginia/Syracuse line had a lot of movement around gametime, so don't quote me on who ended up being the favorite in that game, but I'm fairly certain either every single or almost every single Big 12 team was an underdog for their bowl game. (Dallas Morning News)

Examples of facetious usage:

Roughly speaking, there are 1,000,000 yoga teachers in London alone and only 100,000 studios (don't quote me on those statistics). (The Daily Telegraph)

We in the West scoff our Pop Tarts (surely descended from the Cornish pasty? Don’t quote me on that!)… (The Independent)

The identical expression exists in English, but it deals with specificity or the ease of categorization rather than truth or accuracy:

Unfortunately, this guess can't be nailed down without lots of additional research. — “Something is flashing brightly in deep space and scientists have no idea why,” BGR.com, 4 Apr. 2018.

But on Tuesday, he said “I can't be nailed down today on the specifics of what I might or might not run for.” — “Howard Schultz on presidential speculation: ‘Let's see what happens,’” CNBC.com, 5 June 2018.

The answer isn't that simple, it can't be nailed down to just one particular issue or one reason. — “This is Why Farmland Prices Really Won't Come Down,” DreamDirt blog, 14 Jan. 2018.

There are several equivalents in English for introducing a rough guess/estimate or any statement whose accuracy a speaker is unable to vouch for. Perhaps the most common one is “Don’t hold me to it…”

We have about a half a million people, I think. Don't hold me to it. — Culture and countries, Tulsa, LingQ

“Where is that big-headed husband of yours?” Tonee asked Keylona. “Don't hold me to it, but he said he had a lot of work he had to get done around the office today.” — Chillee Willee, Say It Isn’t So, 2010.

“Can’t say for certain, and I sure as hell couldn’t testify to it, you know, under oath or anything like that.”

“I doubt you'll ever have to.”

“All right, long as you don’t hold me to it. I’d say it started in the parlor on the ground floor. Somebody put a candle too close to a curtain in the front window, the curtain caught fire, and the whole place went up. I got no proof of that, of course, but I did find the brass candlestick.” — Christopher C. Gibbs, Rest Her Soul: A James Buckner Novel, 2012.

The firefighter in this novel manages to hedge his guess about what started a fire with three expressions:

Can’t be certain

I couldn’t testify to it (more common: couldn’t to it)

Don’t hold me to it