Pootle has the ability to display alternative source languages while translating. Thus, translators who know another language better than English can take part in the translation project. Also, it provides a way to disambiguate terminology seeing how other languages have translated the same translation unit.
Users who want to use the functionality need to specify the desired alternative source languages in their account configuration.
Note that if the selected project doesn't have the alternative source language it can't be displayed.
This feature is enabled by default, but alternatively, Pootle server administrators can disable this feature by setting
ENABLE_ALT_SRC = False
in pootle/settings.py. For Pootle 1.2, set
enablealtsrc="False"
in pootle.prefs.