Native? Polish. In a way I think German also qualifies since my mother is and was often talking in it, even when I was basically picking up the speech as an infant, but it's a language that I can rarely (if ever) exercise. I have learned some Czech from my neighbour who was also my piano teacher and I happen to know a bit of Swedish that was enough to confuse a true Swede if you don't mind that exaggeration ;).

Polish as a native language makes it very hard to get used to puns. We have very little to show when it comes to homophones and homonyms. Plus we don't really have prepositions like 'a', 'an' or 'the'. In Polish you use suffixes and context to signify whatever preposition does. It makes most foreigners scratch their heads since word like "Michała" can mean (depending on context) "Property of Mike", "Made by Mike", "Mike's" or "Feminine form of Michael that functions here as a name of a person". Plus it seems that every qualifier I'm making is strong as it can get in English while in Polish it would be more context-sensitive.

what coding

UTF-8 :P. Otherwise the above example will look like complete crap.

Do you sometimes think in this language, rather than your native tongue?

This is weird, but bare with me: I'm rarely using words when I think of something. It's more of a matter of connections between shapes, sounds or memories. When I think "Cat" I see a picture of one, a picture of encyclopedia entry on one as a literal picture etc. I'm rarely using sounds for anything in my head. I have problems with differentiating people by voice etc. I don't know why, but it's a lot of like library in my head. Most of the time when I talk, as you could see in the recording you referenced, I have long and mostly silent pauses. That's my brain trying to interpret Devac's Headspace(TM) to speech. Plus I was nervous as hell which does not help much.

Bit artsy/autistic description, but that's how it seems to work for me. If I 'hear' myself in the head it's usually the language I'm focusing on. If I'm learning/speaking English, it's English etc.