Death Note (2017)
There is no such language as Celtic, rather there is a Celtic family of languages. Extant Celtic languages include: Irish, Welsh, and Breton.
'Kira' doesn't mean light is any of these languages, in Irish for example the word is 'Solas'. Futher most Celtic languages don't even use the letter 'K'.
Errors in geography
Incorrectly regarded as goofs
Correction - Ryuk is referring to someone writing his name to be killed, since what we saw was just a warning this is why the writer wasn't killed before he/she could finish.
Correction - What we saw written was a warning not a notice of death, a Death Note of you will, so maybe there's different rules for that (there is a lot of rules after all) Plus who says Ryuk is his real name.