How do you know what the standards for expenses are if the taxpayer lives in a foreign country?

According to the Internal Revenue Manual:
The Allowable Living Expense standards are not available for international taxpayers or the U.S. Territories, except for housing and utilities in Puerto Rico. In the absence of standardized figures for foreign countries, a fair and consistent approach should be applied to what is allowed as living expenses for international taxpayers.
Our recommendation is to identify a US city that has living expense standards similar to the foreign location the taxpayer resides. For instance, the cost of living in Hong Kong, according to online searches, is similar to that of New York City. If my client lived in Hong Kong I would use the New York City standards and explain this in my cover letter.
Our experience is that this approach works with the IRS, just be sure to explain in your cover letter your rationale for using the standards you used in formulating your Offer.