Hi, and thank you for your interest!
yast-installation is being translated using Weblate, a web tool designed to ease translating for both developers and translators.
Translation project for yast-installation into English (United States) currently contains 341 strings for translation and is 1.1% complete.
If you would like to contribute to translation of yast-installation, you need to register on this server.
Once you have activated your account just proceed to the translation section.