Like zenith, garble has a complicated history, from Latin to Arabic then back to Latin. Its first meaning in English is "sift, take the pick of", then it came to mean "make selection from (unfairly or with a bias)". Its modern meaning, at least for me, is "mix up or distort to such an extent as to make misleading or incomprehensible". It's from Anglo-Latin garbellāre "to sift", from Arabic ġarbala "to select", from غربال ġirbāl "sieve". And ġirbāl was perhaps borrowed from Latin crībellum, a diminuitive of crībum "sieve". The PIE root is *krei- "sieve, discriminate, distinguish".
The suffixed form *krei-men- became Latin crīmen "judgment, crime". This combined with dis- "apart" to form discrīmen "distinction" and discrīmināre, borrowed into English as discriminate.
From "discriminate, distinguish" to "garble". That's quite the semantic spread.