It's possible to filter the translations added by a user to a particular language in a POEditor project in two pages.
How to filter translations by user in the Stats page
If you're the project owner or an admin, you can filter the translations added by you or other users in Stats > Reports by Contributors, clicking on the name of the contributor and then on the eye icon next to the language of interest
You can do the same thing in Stats > Reports by Contributors, after clicking on the language of interest, and then on the eye icon next to the user whose translations you want to see.
If you are a contributor assigned to one or more languages in a project, you can also go to Stats section and click on the eye icon next to any language to filter the translations you added to that language in that project.
You can remove this filter clicking the X next to contributor filter in the section Show.
How to filter translation by user in the Contributors page
If you have the role owner or admin in a project, you can also filter the translations added by contributors from the Contributors page. Next to each language, there's an eye icon you can click on to filter the translations.
These filters are not available in the Contributors page for users with the project admin or project owner roles, because these roles have access to all the languages in the project and the languages are not listed for them in this page.