[gaur]

> I'd argue "per annum" or p.a. isn't a foreign term and just standard English.

Did you notice that a fluent English speaker had to ask what "p.a." meant? Do you think that would have happened if it had been written "per year" instead?

[adenadel]

The same could be argued for any jargon outside of one's own field.

[Tomte]

As a counterpoint: I'm not a native English speaker, I do understand "yr" just fine, but it takes me a split second longer to read that abbreviation.

Because p.a. is also part of my language.

[edoceo]

How could one tell the OP was fluent?