That's a known issue with the PAL version of Mario 64. You can fix it by using Rice's Video plugin 5.5.1 from the download-section, or by downloading the American version (I won't tell you where to get it).
I got both the euro and the US version of the rom. They both ask me to choose a language at the begining.... and have the no text problem. Perhaps my US version is mislabled?
I got the Rice plugin like you suggested but I get an error when I open Nemu64 that says it couldn't load the DLL.