What your first language does to the new one
Most of an accent is not laziness or a bad ear — it is your first language reaching for the nearest sound it already owns. Meet a sound your language does not have and your mouth substitutes the closest one it knows, usually without you hearing it happen. Pick the language you grew up with and the one you are learning: this works out which sounds are missing, which sound you will reach for instead, and which pairs of words you are likely to say identically.
Every pair below is computed from the two languages' sound inventories — not from a list of "common mistakes". That means it covers all 240 directions, including the ones no textbook is written for.
I speak English English
I speak French Français
I speak Spanish Español
I speak Portuguese Português
I speak German Deutsch
I speak Italian Italiano
I speak Georgian ქართული
I speak Russian Русский
I speak Hindi हिन्दी
I speak Mandarin Chinese 普通话
I speak Cantonese 廣東話
I speak Vietnamese Tiếng Việt
I speak Korean 한국어
I speak Japanese 日本語
I speak Malay Bahasa Melayu
I speak Turkish Türkçe
The number is how many sounds that language has that yours does not.