A few days ago, Ivan Seoane showed me weblate - an open source translation management system. Very nice and very suitable for OpenStreetBrowser. I installed it right away, you can find it here: https://weblate.openstreetbrowser.org. Also, Ivan is working on the translation for Galician, which is already available.
Be aware, that authentication is not connected to any other service (like OpenStreetMap, OpenStreetBrowser Dev, Github, Weblate), so you need a separate account there.
Not all parts of OpenStreetBrowser can be translated there, e.g. date formats have their own separate repository, as you have to actually produce code (it’s just too complex).