四海之内皆兄弟

all men are brothers

four / 4

surname Hai

ocean / sea / CL:個|个[ge4],片[pian4] / great number of people or things / (dialect) numerous

(possessive particle, literary equivalent of 的[de5]) / him / her / it

inside / within

inside / inner / internal / within / interior

all / each and every / in all cases

elder brother

brothers / younger brother / CL:個|个[ge4] / I, me (humble term used by men in public speech) / brotherly / fraternal

younger brother / junior male / I (modest word in letter)

variant of 悌[ti4]