Given the amount of thought and effort I've put into creating aspects of the Alpennian language, it might seem strange that so little of it appears in the books themselves. Other than proper names, most of what readers have seen have been the occasional technical terms that don't have a simple English equivalent (armin, markein, vizeino). I'm not counting all the Latin terms used for mysteries, of course.
A major reason for this is the principle that, in theory, the stories are entirely "translated" from Alpennian, and that therefore any time a character is thinking or speaking in their native tongue, it should be rendered transparently in English. I occasionally throw in non-English words and phrases when a character is speaking something other than Alpennian, as when Jeanne self-consciously uses French words and phrases. But within Alpennian itself, I have to find other ways of reminding the reader that we're in the midst of a different culture.
One of the things I've done is to have characters take words or phrases that relate to special aspects of their experience and use them in extended, more everyday senses. An example of this is how characters use the word "ambit." This is an ordinary (more or less) English word meaning "the scope, extent, or range of something." I've established it as being an ordinary technical term from the structure of mysteries meaning "the defined bounds or scope within with a mystery is intended to take effect." But then, having established that, I show characters using it (in both speech and thought) for a more general sense of "the sphere of influence or responsibility of some person or institution." So, for example, a person's place of residence will place them within the "ambit" of a particular local church. Or when Barbara thinks about the people she feels a nebulous sense of responsibility for, she thinks of them as being "within her ambit." The intent is to indicate that this word is translating an Alpennian term that has a set of meanings that don't correspond exactly to a more common English word. At the same time, the intent is to connect that word with the pervasive presence of mysteries in Alpennian lives, such that even people who have no sensitivity to mystical forces, will think about other aspects of their lives with the same concepts.
A more extreme version of this sort of idiomatic word use is the "literal translation" of Alpennian idioms or sayings. One that I've used in several of the stories is the phrase "to trespass in someone's garden" with a sense equivalent to "to step on someone's toes, to give offense by violating someone's sense of social 'ownership' of a person, idea, or activity." The literal meaning makes it easy to work out the figurative sense, but it isn't a fixed saying in English the way it's being used. That gives it the ever-so-slightly-off-balance sense of translating another culture that I'm aiming for, without tripping the reader up too badly. Alternately, I might make a figurative phrase like this "more Alpennian" by using a different wording than the familiar English expression. For example, rather than a person saying, "I know which side my bread is buttered on," I have a character saying, "I know where the butter for my bread comes from."
Similarly to that sort of elaborate "literal translation" are a few turns of phrase I've established as "Alpennian idiom" that are closer to being grammatical quirks than meaningful phrases. One that I've used in several of the books is the phrase "to do for" as indicating a fairly specific personal relationship between a servant or attendant and their employer. So, for example, an armin "does for" the person he protects. A valet or lady's maid "does for" the specific person they serve. But you wouldn't use the phrase about a more general household servant like a footman or a kitchen maid. Another example in this category is, "It doesn't belong to you to do X" with the meaning "It's none of your business to do X, it isn't your responsibility" but with a sense of intrusion and butting in.
The idea here isn't to constantly bombard the reader with unfamiliar turns of phrase and jargon, but to lightly season the prose with reminders that this is a different culture with different ways of thinking and talking about things. Ways that will influence far more than just the words they use.