There's no point if it doesn't get through to English speakers.
Literal
English speakers [to-に] understood-[obligation negative-なきゃ] meaning not-exist [emphatic-ぞ].
英語話者 'English speakers.' 通じなきゃ 'if it doesn't get through' — casual conditional of 通じる 'to be understood/to communicate.' 意味ないぞ 'there's no point' with masculine emphatic ぞ. Blunt, practical language-learning truth.