"I wonder if entries like
expertise [tech.] - die Begutachtung
expertise - das Gutachten
expertise - das Sachverständigengutachten
expertise - Gutachten eines Sachverständigen
are intended to refer to the skill or the action in general (noncountable) rather than a written document (countable)."
No, unlike Sachverstand, Fachkenntnis etc. (valid translations for 'expertise') they do not refer to the skill itself but to the application of this skill or the result thereof. So they are all misleading.
@ CJ: "Maybe its too late in the evening, but I cannot seem to follow your line of reasoning. If expertise can mean expert opinion, I see no reason to delete the entry expertise die Expertise, though it might be useful to mark the English side as [rare]."
First, I said "even if expertise can mean an expert's opinion" (referring to entry 1 in MW cited in #1, Chambers cited in #2), nobody has come up with examples which show that it can be used like "Gutachten". Up till now Vahlen Wirtschaftswörterbuch (cited in #2) is the only printed source which says that expertise can mean 'expert's report' in BE, but nobody has found evidence that it can.
Second, I said, even if it can, you can't translate expertise as Expertise (or Gutachten and the like): The concepts behind the two words are totally different and it is misleading to offer one as a translation for the other.
How is Expertise or Gutachten used? Brockhaus/Wahrig says: (entry Expertise) "eine ~ einholen, erstellen lassen (über etwas); jmdn. mit einer ~ beauftragen"; (entry Gutachten) "ärztliches, sachverständiges, schriftliches ~; ein ~ (über jmdn. oder etwas) abgeben; von jmdm. ein (zweites) ~ einholen; zur Erstattung eines ~s bestellt sein."
You can think of any number of correct German sentences which would turn out wrong in English if somebody looked up Gutachten or Expertise in Leo and used expertise. Unless of course you consider the following correct in English:
She asked another doctor for a second expertise.
He ordered an expertise to be made.
The psychiatrist's expertise was read out in court.
The two medical expertises came to different results.
According to one expertise, the painting was an authentic Vermeer, according to the other, it wasn't.
The other way round: According to Dr. Frankenstein's expertise, the creation of artificial life is feasible. If this sentence is correct. 'expertise', in this case, means 'an expert's opinion', but you can't translate it as either Gutachten or Expertise.
P.S.: I think Lothar put it very well not only as far as the legal part is concerned: Gutachten ist immer das Ergebnis der Tätigkeit, in der der Gutachter seinen Sachverstand einsetzt. That's why Gutachten and expertise demand completely different syntactical structures. The same is true for Begutachtung, although this word emphasizes the activity rather than the result of the activity. Eine Begutachtung durchführen -- you can't carry out an expertise. The idea which governs the English word is the competence behind an activity (Begutachtung) or the result of the activity (an oral or written statement); the idea behind the German words is the activity or the statement itself.