How can I know who changed an English message?

The source is git. mw:Gerrit/Navigation#System_messages answers your question for MediaWiki; for the other projects you have to check the respective repositories, which are generally linked from the project page like Translating:OpenStreetMap.

Nemo (talk)22:34, 6 July 2016

Thank you for the answer.

Guycn2 · 02:11, 7 July 2016