You need to look further than the currency location of the company. What is more important is where the revenue of a company comes from. An example is a UK telecommunications company traded on the LSE in sterling. Way more than 50% of its revenue comes from outside the UK.
As for the right approach, I don't think there really is an answer as it all depends on your risk tolerance. Personally I have 30% of my investments in gold, silver and mining stocks, less than 10% cash and the rest in equities. The equities are about 70% European companies with large exposure to Asia (at least 30% of revenue), and 30% Canadian oil and gas income stocks. I believe that this would be considered risky by many people, but based on my economic beliefs I see this as reducing risk.
Bottom line, look at where the revue comes from do work out the currency risk.