It's reasonable to assume they're broadly stable, but being broadly stable doesn't mean a drop will "recover". There's no specific ratio that the currencies are being pushed to. Permanent changes in the baseline can and do happen.
> You're buying a share of productive capacity, the currency it is listed in doesn't matter.
But I don't own a fixed percentage of production, I own a fixed number of shares and the number of shares can change. If the number of shares doubles, then my investment is worth half as much.
This is correct. A decent example would be comparing the CHF, EUR, USD over the last few decades. The CHF is to the EUR what the EUR is to the USD.
> But I don't own a fixed percentage of production, I own a fixed number of shares and the number of shares can change. If the number of shares doubles, then my investment is worth half as much.
How is that related to currency changes? That can happen anyway regardless of the currency.