From all I have studied, the most accurate way to go is to use your name as listed on your birth certificate. Nicknames or names adopted later (marriage, name changes, etc.) give a vibration for that time period, but the birth name is the true character of your being.
When I am doing reports for people with two surnames, I join them together (this matters more for essence and transits than for core numbers). I do the same for a person with two middle names.
The question about the use of other language's alphabets is interesting. I have thought of this, but I have no answer. But obviously, English is not the first language that has applied the use of numerology. China, Egypt, Greece...they all used the science of numerology thousands of years ago. It has just been converted to English at some point in time. Maybe someone else here has studied more of the historical aspects of it and can say what to do about foreign letters.
