Spock still speak human language in logical sense without emotion.
That's his character. It's a hard question to answer, because it requires significant sociolinguistic knowledge. It falls under the same concept of why gay people speak so effeminately. People often incorporate elements of multiple styles into their speech, either consciously or subconsciously, thereby creating a new style. That being said, it's hard to define Spoke's direct tone and style.
I did some research on according to William Labov, who studied individual linguistic variables, and how they were associated with various social groups (e.g. social classes) summed up his ideas about style in five principles:
Keep in mind my knowledge is this topic is nonexistent.
"There are no single style speakers."
Style-shifting occurs in all speakers to a different degree; interlocutors regularly and consistently change their linguistic forms according to context.
"Styles can be ranged along a single dimension, measured by the amount of attention paid to speech."
Style-shifting correlates strongly with the amount of attention paid to speech. According to studies conducted by Labov, this was one of the single most important factors that determined whether or not an interlocutor would make a style-shift.
"The vernacular, in which the minimum attention is paid to speech, provides the most systematic data for linguistic analysis."
Labov characterized the vernacular as the original base mode of speech, learned at a very young age, on which more complex styles build later in life. This "basic" style has the least variation, and provides the most general account of the style of a given group.
"Any systematic observation of a speaker defines a formal context where more than the minimum attention is paid to speech."
In other words, even formal face-to-face interviews severely limit a speaker’s use of their vernacular style. An interlocutor’s vernacular style is most likely displayed if they do not perceive outside observers, and are not paying immediate attention to their own speech.
"Face-to-face interviews are the only means of obtaining the volume and quality of recorded speech that is needed for quantitative analysis."
Quantitative analysis requires the kind of data that must be obtained in a very obvious, formal way.
Feel free to review the link below:
https://en.wikipedia.org/wiki/Style_(sociolinguistics)