Are these phrases too posh-sounding for conversational English?

I'm German, and I try to speak British English as best I can, it's the language I've learned at school, and I'm always trying to be consistent. However, much of my English vocabulary and phrasing I picked up from British television programmes, films and books. Which is why I often use phrases like these:

• It's not at all confusing

• Thank you very much indeed

I also use the British English spelling even if both forms are accepted and in use:

Right click to open the Preferences dialogue

And even mix the two if needed:

You need to set the --color=always argument so that colours are escaped properly

My question therefore: Do I sound posh? Does my language come across as professorial or holier-than-thou? If so, what can I do to sound more appropriate?

Please underpin your answers with some references. This is not meant to be a discussion of opinion; I'm sure there is some evidence available on the subject.^{(Or vote to close it as argumentative if you disagree)}

For technical documentations, you can sound as sophisticated as you want: if the reader gets immediately what he/she is supposed to do, it doesn't matter.

I would however follow the advices of “The Elements of International English Style” by Edmond Weiss, as they refer to a more "neutral" form of English, which has greater chance to be understood by any reader.

• write with sentence simple enough to understand without any ambiguity (i.e., the Principle of Simplicity).
• write with sentence clear enough to understand without any ambiguity (i.e., the Principle of Clarity).
• reduce the visual burden of reading due to lazy punctuation, page layout, or a combination of other factors (i.e., the Principle of Reducing the Burden).

The last chapter addresses the inescapable need for cultural adaptation.
Even if one is a master of English he or she can still make errors in technical documentation of the cultural context is ignored.

It's really hard to judge your command of the language based on your writing alone. To properly answer this question, native speakers would need to listen to you having a conversation.

That being said, you are using "posh sounding" words (professorial, underpin) incorrectly in your question, or at least not as a native speaker would. This makes it read as if you were using a thesaurus to come up with these words. Rather than seeming posh, your writing reads awkwardly and has a somewhat pretentious feel to it.

EDIT: To explain what I mean by incorrect use of professorial and underpin.

Underpin: @invariant says it best in the comments: a native speaker would say "support" or "back up" in this situation. Underpin is really never used as a command. A native speaker, instead, would refer to the "underpinnings" of something: the "foundation" upon which it is built. The theoretical underpinnings of calculus are difficult for new students to understand. A native speaker might also say that something underpins something else. Xenophobia underpins the recent gains made by the Party for Freedom.

Professorial: The OP seems to be using "professorial" to mean "aloof", "distant", "arrogant", or something similar here, which are things a native speaker might say. Professorial, as an adjective, does not necessarily imply any of those things. As far as I'm aware, it has no clear and generally accepted connotation. In most of the example usage of "professorial" that you find with Google, the word is used to describe things directly related to or done by professors: professorial entrepreneurship, professorial fashions, professorial lectures, professorial sabbaticals, etc.

Be very wary of the confusion between sounding posh and sounding educated.

The two are highly confused in British society at the moment, as there is a culture of disrespect for education amongst a large section of the populous.

There are modes of speech that indicate an educated tongue, particularly use of lesser used words, for instance, underpin in the question. A strong vocabulary often sits with a good standard of education. Also, use of archaic words and a rhetorical style tend to indicate a greater enjoyment of word play, as opposed to sounding "posh" at all.

The concept of speaking in a "posh" fashion is more to do with affectations, pronunciation, cultural inclusions unfamiliar to the rank and file.

A sentence such as "I say, did you see the performance of Carmen this season? Superb I felt." sounds posh, due to the content and style, not the vocabulary in play. If delivered in RP, then all the more so.

Sounding "holier-than-thou" is also a distance apart from sounding posh. That phrase tends to indicate talking down to someone, condescending content to the speech, with a refined air that indicates distaste and superiority. That can come over without any element of being "posh", particularly from strongly religious folk.

It is not my place to comment on your use of language, because I am in a similar situation. I will say a few things that are only partly on topic.

I have been told by some that the quality of academic English, even by native speakers, is often not that great, and that those well versed in literature will sometimes cringe at its verbosity and formulaic phrasing. So the English of a foreigner need not be worse than that of a native speaker, nor should he blindly follow a native speaker's lead.

One reason for this is the fact that there are numerous "schools" in any language: some say the split infinitive is all right, others call it anathema; some consider the past subjunctive dead and buried, others insist upon it; etc. There is probably an "average" group that has certain opinions, and several other, smaller groups that have other opinions. Such a group sometimes condemns what is common practice in another group; this should not be mistaken for what is universally condemned because it sounds foreign, which it is indeed undesirable for anyone.

In my language (Dutch), for example, I believe that some would consider my usage a tiny bit old fashioned and unusual, occasionally. This does not concern me; it is the way I was brought up, it is the way my family speaks and many of my old friends. However, because we are a minority, a foreigner speaking Dutch might be "corrected" by other native speakers if he learnt to speak as I do. Because they do not get my language, they do not get it in a foreigner, and they might say that he was using unusual idioms.

Should this foreigner be concerned? I believe not, though I can imagine that others might disagree. Even so, it is generally not a bad idea to avoid sounding too conspicuous in any way: if you are aware of the fact that a phrase sounds very unusual, it might be a good idea to change it; striving after a balance is never wrong.

I believe that, at least in conservative circles in Northern Europe, the trend has long been to use plain words as much as possible, to avoid using words more complicated or unusual than necessary. I can vouch for those in modern-day Holland and England, and, since this was also the case in the Latin of the age of Cicero, I believe it to be a somewhat universal tendency that may rise in various circumstances at various times. I have also seen signs of this trend in German.

How this tendency manifests itself depends on many things. In English, it means that a writer should be alert when using many words that come from Latin, many proverbs, metaphors, local idioms, passive constructions, novel words, abstract nouns, noun adjectives, etc. This is not to say that he should not use any of those, which is impossible: just that he should not use them too often or in the wrong places. Several branches of this trend have developed in non-conservative circles too, though they are sometimes less rigorous.

So it is best for a foreigner to resist the use of "sophisticated" words for no reason, and use them only when he feels sure that they express his intentions better than simpler words. I do what I can, but resistance is not always easy. Even so, abstaining from any and all idioms and abstractions for fear of doing it wrong will, I believe, generally result in language of lower quality than would taking some risks.

P.S. I am always trying to improve my English, so please feel free to post any tips on my language in the comments. I know I must be making mistakes, and it is hard to correct them if nobody will point them out.