If no AUser Manager translation is available for your language, you need to create one from scratch. Ensure you have already installed the Joomla Core translation of your language. You will notice a "languages" directory with two folders, "admin" and "site". In each of this folders an en-GB.com_auser.ini file is located. Rename them that they match with your language tag. For a German translation that would be "de-DE.com_auser.ini" for example. Now you can start the translation process. To do so, open the file with an editor of your choice. Take care when saving. The file need to be saved in UTF-8 without BOM. If you have finished translation, copy the files to your Joomla as described above.
Please share your work like we do with AUser Manager itself and make your translation available for others speaking you language. Just mail us info_at_alikonweb.it and attach your work.
Thanks.