The norm in most of my interviews has been that candidates can solve coding problems in whatever language they are most comfortable with.
I assume they've already filtered out candidates whose "most comfortable language" isn't the one they're hiring for, or they're going to have a difficult time when they come across the one who wants to use APL or x86 Asm.
I heard a tale of a candidate white boarding in an obscure language (in a bit of an attempt to hide a deficiency), unfortunately for the candidate the interviewer happened to be well versed in the language and saw right through the charade.
Hah. Even if the interviewer didn't see through the charade they have plenty of time to check the code after the fact. Once or twice a candidate has done something I didn't know about so I just googled it. Nice little learning opportunity for me.
I assume they've already filtered out candidates whose "most comfortable language" isn't the one they're hiring for, or they're going to have a difficult time when they come across the one who wants to use APL or x86 Asm.