It's clear that to get good diversification we need to add other currencies to our portfolio. It can be done through 2 different ways:
1) Considering "currencies" as an asset class. In this case we hold bonds, shares, real estate and... a percentage in a basket of currencies. For instance, we buy a monetary fund in Swiss francs and some ETFs of kronas or Australian dollars.
2) Considering currencies as an another layer in the rest of asset classes. This is our favorite approach. In our book we recommend for the cash (short term bonds) and stock part a distribution of 30% of money in different currencies. So, as an example, if we are leaving in Europe and we mainly own German stocks, we should buy some US, Australian, Hong Kong shares to diversify. Through foreign shares we are using other currencies.
Given the increased uncertainty about the global monetary system and big shifts taking place in the structure of the World economy, currency diversification is a must against global shocks and to maintain long-term purchasing power.