Hello Polyglots, you can start translating WordPress 4.5!
The strings are in the Development project at https://translate.wordpress.org/projects/wp/dev. The strings for WordPress 4.4 have been moved to https://translate.wordpress.org/projects/wp/4.4.x. Please note that there are a few fuzzy strings which might be a good starting point for WordPress 4.5.
WordPress 4.5 is planned for April 2016. Happy Translating!