What you're trying to achieve with long-term savings is to support a future lifestyle. That future lifestyle will be in some retirement country (not necessarily Singapore -- you have to figure that out at some point), and with some blend of non-local spending. For example, you might spend two months per year spending in Swiss francs and euro, skiiing the Alps. The currencies you need to exchange for goods and services to support your future lifestyle are then important. But they're not important until then.
I fundamentally agree with Vanguard's approach in their "Target Retirement" funds. They hold the global equities allocation of the "Target" portfolios steady until 7 years before the target date, then starting at that point they make their gradual, progressive shift to a 30%/70% stocks/bonds allocation by the time the target date is reached. That's then the drawdown portfolio allocation, designed to support years and decades of funding for a retirement lifestyle. (Not designed to be withdrawn all at once, please note.) The bonds are, of course, U.S. dollar denominated bonds -- Vanguard U.S. is catering to those who are retiring in the U.S. Emergency reserve funds should be highly correlated with the currency of the country(ies) where you have a right of abode.
So, "Don't worry," basically. As long as your investments are prudent (well diversified) and age appropriate, and as long as you start a gradual adjustment to a drawdown posture at 7 years before drawdown age (or up to 10 years before if you're very conservative), that'll work fine. Moreover, you might not be sure where you'll retire, so I wouldn't make such decisions all the way up front at age 25, for example. Here's where I differ with ST a bit, perhaps. I don't like overweighting Singapore listed stocks as much as/as early as ST does. I feel more comfortable for those with a right of abode in Singapore expecting to retire in Singapore to overweight ES3 only somewhat (e.g. up to 20% of stocks), then more aggressively overweight ES3 within the 7 to 10 year portfolio rebalancing before drawdown age. So something like this:
Accumulation Phase: 20% bonds/bond-likes (MBH, SSBs, CPF), 80% stocks/stock-likes (of which up to 20%, i.e. 16%, is ES3 and the rest in IWDA, IWDA+EIMI, or VWRD, plus your primary HDB residence typically)
....gradually adjusting within the 7 to 10 year period before Drawdown Age to....
Drawdown Phase: 70% bonds (MBH, SSBs), 30% stocks (split 50-50 between ES3 and global stocks)
I'm just flat out uncomfortable with what I view as too much overweighting of ES3 during one's Accumulation Phase, in part because of the Japanese experience and also the fact the SGX isn't likely to have any meaningful future Apples, Alphabets, Amazons, etc. -- no IPOs. I don't have a perfect crystal ball, but it's reasonable to forecast that the SGX will be a relatively low capital gains, dividend-oriented play, and that's not something I recommend overweighting during one's Accumulation Phase.
One other assumption I'm making here is that you're dealing with quality currencies. You should skip low quality currencies, except for immediate, on-the-fly spending needs. I currently wouldn't want to have really any fraction of wealth in Venezuela's currency (or currency correlates), for example. Fortunately, the Singapore dollar is a high quality currency, and that's a major advantage for Singapore resident investors. MAS manages the Singapore dollar as a trade-weighted basket of currencies, with some volatility dampening applied, and that works!