How Could I say "Bachiller académico" in english?
"Bachiller Académico" is the degree obtained after high school.

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I think in Colombia a Bachiller Académico means a "High School Diploma" (in American English).

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Bachelor degree. (Or undergraduate degree.)

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It would be clearer to say: "Bachiller Académico" is the degree obtained when you complete high school.  In the USA, we call it a "high school diploma".  I'm not sure what it's called in the UK.