How can an EB-5 investor apply through another country that is not their place of birth?

Country of birth controls unless you are married, then you can cross-charge to the country of birth of your spouse. If the question is about processing for an immigrant visa at a US embassy in the country of the second citizenship, then one should be able to transfer the immigrant visa case if one has residence in the country of the second citizenship.

There is no way other than cross-charging by marriage, or in rare exceptions using the missionary exception if born in a country where neither parent was resident.

Always place of birth unless you have a spouse born in another country who is applying with you. Then you can cross-charge to that country.

For a single investor, there is generally no way to apply via another country besides their place of birth. In situations where a birthplace changed nationality (e.g. former Soviet Union to modern day Ukraine) the modern borders will control nation of chargeability. Thus, a person born in pre-Partition India could be counted under Pakistan or Bangladesh''s per-country quota depending on their exact place of birth. If a person is married, and if they are seeking to come to the US together, it is possible to "cross charge" and use the birthplace of their spouse. This is subject to numerous limitations, so it is advisable to consult with an immigration attorney in such a situation.

Your country of birth will always control your country of chargeability for visa issuance purposes. If your spouse was born in a different country, you can use the principle of cross-chargeability and make use of her country of birth for visa issuance purposes so long as you are applying for green cards at the same time.

No, there is no other way.

The visa availability depends on place of birth. If you want to change that, then you can use the place of birth for your spouse.