Spock was raised in a bilingual household, his father was an ambassador to Earth, and his mother, at least according to unofficial sources, was a linguist. It stands to reason that he learned both English and Vulcan from childhood. People raised in bilingual households are often fluent in both their parents' languages and can code-switch between them on a dime.
B'Elanna, similarly, probably learned both English and Klingon as she grew up, but she identifies with her human side and lives in the Federation, and thus presumably prefers English. I don't recall her ever speaking Spanish.
As an aside, the language used by the Federation (or at least the humans) is referred to as Linguacode in at least Star Trek: The Motion Picture, and possibly a few other episodes or films.
No, linguacode is not the language they speak. It's a protocol for computer translation when making first contact with a new species, a method for building a translation matrix quickly from basic principles. "In a Mirror, Darkly" established that Hoshi Sato invented it in the 2160s.
Linguacode was a translation matrix used during first contact scenarios, often employed when the universal translator was unable to facilitate communication. The language was developed by noted communications officer Hoshi Sato in the 2160s. (ENT: "In a Mirror, Darkly, Part II") It was generally...
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The language the Trek characters speak has always been identified as English, except in a couple of recent productions which have referred to it as "Federation Standard," a term previously only used in tie-in fiction or fanfiction.
My assumption is that almost everyone in Starfleet working on majority human vessels or bases is speaking English, as it makes sense for a crew to have a common language when they're all space scientists expected to understand and obey exact orders in crisis situations.
Yes, absolutely. The assumption that the crewmembers are all speaking their native languages and using translators to communicate all the time is ridiculous. First of all, technology can fail, and Starfleet would surely want its officers to be able to cope with situations where they can't rely on their machines. Second, even the most perfect computer translation will not be completely accurate, since no two languages map perfectly onto each other (although fiction tends to gloss this over for convenience). Some nuance and precision will always be lost. The only way to avoid misunderstandings is if everyone's fluent in the same language.
Also, though the shows and films tend to use the dramatic shorthand of having actors deliver "translated" dialogue in English, it would realistically work more like it was shown to work in
Beyond, with the original language still audible under the translation. That would get confusing in a situation where a lot of people were talking right after each other, giving reports in quick succession, with the translation voices overlapping. Clarity would be better if everyone's speaking the same language.