1. Go to wordpress/wp-content/plugins/wp-user/languages directory
2. Copy the file wpuser-en_US.po
3.Rename it according to language code. (ex. If you want to translate into German then file name will be wpuser-de_DE.po)
4. Open the file Add the translation for the every msgid.( Enter your translation text in to msgstr )
5. Save the file
6.Then create new .mo file using http://po2mo.net and save it into plugins/wp-user/languages folder.