We know we let MAME’s translation files rot for almost a year, and for that we’re truly sorry (the technical reason is lack of C++14 support in GNU xgettext), but we’ll be in much better shape on this front for our next release (0.189 scheduled for 30 August). The Chinese, Greek, Brazilian Portuguese, and Spanish translations are up-to-date or very close to it, thanks to A. Viloria, Ashura-X, BraiNKilleRGR, Felipé Sanches, and YuiFAN. However, our other translations are still in need of updating.
If you anyone could help out with updating a translation, or contributing a new translation, we’d very much appreciate it. The translation files are in the language folder in MAME’s source tree. Updating a translation doesn’t require programming skills, just knowledge of the terminology in English and the target language, and a text editor with good UTF-8 support. We prefer to receive submissions as pull requests on github – you can contact us on our forum or our IRC channel (#mame on freenode) if you need help with the details. We’d also appreciate reports of localisation/translation issues (on github or our forum).