Forget memorization, you have to understand the reasoning:
The current method is the “agressive accounting” method as all the FX P&L never touches the income statement. Therefore, translating every in the balance sheet item at current rate.
The Temporal method is the “conservative accounting method” as all the FX effect impact the income statement, thus we have to make it as realistic as possible and match the FX with their period of purchase. Thus inventory is average rate, property plant and equipment is historical.
Now, to remember which method to use, if you are functionning in the same currency as the local currency, then you are self-sustained and your parent company is “naturally hedged” against your currency risk as no real conversion ever happens within daily operation. If your operation differ from local then a bunch of FX transalation happen on a daily basis and you are not hedged against FX risk, thus temporal method (the conservative method) must be used.
Hope it helps…