modifiers - Does "so called" have a negative connotation in English?

In some languages the word-by-word translation of "so called" usually has a neutral connotation. E.g. in the Czech language you may very often find a sentence like this (word-by-word translated from a Czech newspaper, not a genuine English text):

1. The government approved exceptions for so called non-pedagogical workers.

Here the "so called" means that what follows is a terminus technicus, a domain specific jargon.

Only sometimes (in the Czech language) in a very specific context it has a negative connotation (and is usually marked with quotation marks in written form or by showing the quotation marks by two fingers of both hands or by changing the intonation in speech):

2. The government does not accept the result of the so called "referendum" in the East Ukraine.

However, I read a recommendation in an English textbook not to use "so called" as it almost always has a negative connotation in English, like in my second example.

The book was written by a native English speaker who had lived for many years in my country and wrote recommendations specific to our locale. In my language we use "so called" by default with a neutral connotation and we usually have to mark a negative connotation somehow, e.g. by intonation. The writer of the textbook, however, advised against using it in English as its default connotation is negative.

Is it true? Do you as native speakers perceive it the same way?

Answer

It's true that OED's first definition for so-called is just called or designated by that name, but the most recent citation for that "neutral" sense is 1863. So even though OED don't explicitly identify it as dated/out-of-fashion, that's what I would say. The "current" definition is...

Called or designated by this name or term, but not properly entitled to it or correctly described by it. Also loosely or catachrestically as a term of abuse.

It's particularly worth noting their most recent citation for that sense...

1980 W. Safire in N.Y. Times Mag. 13 Jan. 6/1
Examples of sneer words are ‘self-proclaimed’, ‘would-be’, ‘purported’ and that Soviet favorite, ‘so-called’.

If William Safire says it's a sneer word, that's good enough for me.

---

Turning to OP's first example, I would say that the "translation" is inherently flawed, since no negative connotations are intended. Depending on context (primarily, the target readership), it might be better rendered as...

1: The government approved exceptions for "non-pedagogical" (non-teaching) workers.
2: The government approved exceptions for workers classified as "non-pedagogical".

Or you could simply omit so-called and leave it at that, for a "neutral" reference. The use of "scare quotes" doesn't necessarily carry negative connotations, so it's a credible way of simply introducing an unfamiliar technical term or usage without it being value-laden.

---

EDIT: In light of the many respondents supporting so-called inaffectionate ¹ use of the expression, I think it's only fair to point out that Google Books claims 1650 instances of "so-called quanta". It's simply not conceivable any of them would be denigrating either the term itself, or its use in the context of some referent undeserving of the label.

In reality there are only 23 instances (of which barely a dozen are visible in context, and within that most are duplicates), and they tend to be older. But it can't be denied that some people still use the term neutrally. So we must be prepared to admit of that possibility if ever we come across a "perplexing" usage.

¹ This is from subscriber-only OED - I can't find an online definition of the usage...
inaffectionate, adj. Obs. rare. Unbiased, unprejudiced.