Thanks,
A
It's my understanding from a Solo 401k investment perspective that currently no special IRS or DOL (Department of Labor) reporting applies when a Solo 401k invests in a foreign company by way of a loan provided the Solo 401k trustee, in this case you, lives in the United States and is a U.S. citizen.
However, the nation in which the Solo 401k investment is being made may have certain restrictions or rule that are beyond my expertise; therefore, you should consult with a tax professional and/or lawyer that specializes in Latvia regulations.
The following two blogs contain more information pertaining to Solo 401k foreign investments.
http://www.mysolo401k.net/Blog-for-MySolo401k.html?entry=solo-401k-foreign-investment-rules
http://mysolo401k.blogspot.com/2012/07/solo-401k-can-be-invested-foreign.html