We do not actually have what could reasonably be called a User Guide. The wiki is an encyclopedic Reference Manual arbitrarily ordered by GUI chunks.
There are YouTube tutorial videos that are more like a User Guide approach.
However, the Gramps Glossary could be considered a scaled down Reference Manual. It is small yet complete enough to be a viable introduction to translate. (We may actually need to begin to trim back some of the entries. They strain the limits of a glossary definition… straying into user guide content.)