Just as a point of interest, I work in the building trade in the UK and when receiving tenders for pricing, the quantities of items on a typical construction industry bill of quantities are often listed for example as: 4 Nr (referring to 4 in number). I have also seen this usage spill over onto tender forms requesting Company Reg Nr, and VAT Nr.

I see this frequently, it's not an isolated occurrence. Here's a link to an example in Laxton's Building Price, Book 2007 - http://books.google.co.uk/books?id=-yGBwbsyVUIC&pg=RA1-PA243&lpg=RA1-PA243&dq=treads+4+Nr&source=bl&ots=_4swPpHFMj&sig=9wuVX_7dXVTa4x_PvkUrvpPV43Y&hl=en&sa=X&ei=0fWBUJnKG46R0QW244CgBQ&redir_esc=y#v=onepage&q=treads%204%20Nr&f=false

"off" even.

'in the UK a boy will say to a girl, “May I take you home”' - oh yeah! in which century?
Rightly or wrongly most of the population of Britain would say "Can I take you home?"

You say take you, I say bring you
You say may I, I say can I
May I, can I, take you, bring you,
Let's call the whole thing of.

I have heard both in the UK. But I am aware that caught fire/catch fire is standard English.

English doesn't use diacritics very often, and certainly not over the letter a. It did use diacritics more in the past, but they have been almost entirely expunged from the language. The are a few left I can think of such as naïve, café, résumé, even now most people simply leave them out. Most of them are of French origin. French diacritics would probably be the only ones that English speakers might be familiar with.

What I would suggest you do instead is change the spelling to Yahna if that is how it is pronounced. If it sounds more like a short o than an open ah (as in Father), then spell it Yonna - like Donna.