You would know where words came from based on the way they're spelt. That would let you know how to pronounce them. It's the exact same thing people do now we just do it without thinking.

The systems at work in English are not nonsensical like people like to parrot. To say it's not phonetic is just wrong on every level as well.

Frankly I'm fine with the historical oddities that have led to modern English. If non native speakers have issues, that's tough luck for them!