RoryLaurie, I am a little puzzled as what you mean by "real" Gaelic.
The word ann means there where I come from, not sure if it's the really useful in this context.
By "real" Gaelic, I mean what native speakers often refer to as "real" Gaelic, or good Gaelic by their personal standard. It refers to a more idiomatic sense of how the language is used that may or may not be conveyed in grammar books. Keep in mind that Scottish Gaelic is not as standardized as other languages, and native speakers will fiercely hold on to their way of speaking, regardless to what any textbook will say. And yes, they will correct you at times, if they don't care for how your Gaelic sounds to them. It's their language after all.
For example, native speakers would more likely say
Tha a' Ghaidhlig air (He has/ speaks
the Gaelic) rather than what you find in most Gaelic language textbook:
Tha Gaidhlig air (He has/speaks Gaelic). Scottish Gaelic is very fond of empathic usage, hence the many emphatic endings for pronouns and a few other words (mi=mise, thu=thusa, a-nis=a-nise) and the empathic use of the definite article. However, as I said above, though these usages are commonplace, they aren't always discussed in more straight forward grammar overviews.
"Ann" in Scottish Gaelic has a number of uses. In some contexts, it does translate to English as "there," as in
Tha cù ann (There is a dog/A dog is there). But it meaning carries over from simply "being there" to "being (there) in something." So it can also covey a sense of something being within something else, within that context or locale, sort of like the English "in," although grammatically, it's not as simple.
To say where I am presently, for example, I would say
Tha mi ann an America (I am in America) or
Tha mi ann an taigh (I am in a house). "An" in this phrase is a sort of helping word here that doesn't really translate into English. But to say
I am in the house, you change it to "anns def art. X" =
Tha mi anns an taigh. "Taigh" is masculine, so its def. art. is "an." But you would know I mean "the house" and not "a house" because I used "anns" rather than "ann." In speech, the difference is empathized by tagging the "s" to the start of following def. art. when you can. So
anns an taigh sounds rather like
ann san taigh.
I don't how how it goes for Irish, but that's how it is with Scottish Gaelic.
Naturally, Scottish Gaelic and Irish have words in common, but like words shared between French and English, these common words can take on different meanings and nuances in each language. I listed examples of "treun" to show how it has been used within Scottish Gaelic.