I figured it out finally. I don't know why but I cant use .class files without putting them in a package. I reworked my structure and finally I can compile my .po file with
msgfmt --java2 -d . -r test.translations translations.po
which will compile the ./translations.po file to test/translations.class giving it the appropriate package information.
Now I can do this
ResourceBundle myRes = ResourceBundle.getBundle("test.translations"); // load my test/translations.class file
GettextResource.gettext(myRes, "message id to translate");
Still got to get the locale working but the essential is there for me right now.
Edit This question helped me to understand that msgfmt was compiling .po files into "real" java objects How to use ResourceBundle