I found this pretty interesting and there may be some historical references to Latvia's history. Is Latvia more or less inspiration to Latveria?
 
Wasn't Jack Kirby born in Latvia?

Jack Kirby was born in New York. lol
 
No, I doubt there is any other connection between the two countries other than Stan and Jack thinking the name sounded cool.

There was a very popular writer or artist in Marvel who was born in Latvia. I can't remember which one. 
 
P.S. That was Gil Kane

No of course Latveria has no similarity to Latvia-which was annexed by the USSR (along with Eastern Poland) under the terms of the 1939 Molotov-Ribbentrop Pact along with Lithuania and Estonia and did not formally regain its independent status until the collapse of the USSR in December 1991!

Terry