First, currencies are not an investment; they are a medium of exchange; that is, you use currency to buy goods and services and/or investments.
The goods and services you intend to buy in your retirement are presumably going to be bought in your country; to buy these you will need your country's currency.
The investments you intend to buy now require the currency of whatever country they are located in. If you want to buy shares in Microsoft you need USD; if you want shares in BHP-Billiton you need AUD or GBP (It is traded on two exchanges), if you want property in Kuwait you need KWD and if you want bonds in your country you need IDR. When you sell these later to buy the goods and services you were saving for you need to convert from whatever currency you get for selling them into whatever currency you need to buy.
When you invest you are taking on risk for which you expect to be compensated for - the higher the risk you take the better the returns had better be because there is always the chance that they will be negative, right down to losing it all if you are unlucky. There is no 100% safe investment; if you want to make sure you get full value for your money spend it all right now!
If you invest overseas then, in addition to all the other investment risks, you are adding currency risk as well. That is, the risk that when you redeem your investments the overseas currency will have fallen relative you your currency.
One of the best ways of mitigating risk is diversification; which allows the same return at a lower risk (or a higher return at the same risk). A pure equity portfolio is not diversified across asset classes (hopefully it is diversified across the equities). Equities are a high risk-high yield class; particularly in a developing economy like Indonesia. If you are very young with a decades long investment horizon this may be OK but even then, a diversified portfolio will probably offer better rewards at the same risk.
Diversifying into local cash, bonds and property with a little foreign equities, bonds and property will serve you better than worrying about the strength of the IDR.
Oh, and pay a professional for some real advice rather than listening to strangers on the internet.