([Full Changelog](https://github.com/jupyterlab/jupyterlab/compare/v4.0.0a6...0350c6e6cafa06e0a4903507524789d938b75710))
Enhancements made
- Add editable selector [10957](https://github.com/jupyterlab/jupyterlab/pull/10957) ([krassowska](https://github.com/krassowska))
- Removed debug switch, added bug button state update [10727](https://github.com/jupyterlab/jupyterlab/pull/10727) ([3coins](https://github.com/3coins))
- Add debugger variable renderer based on mime type [10299](https://github.com/jupyterlab/jupyterlab/pull/10299) ([fcollonval](https://github.com/fcollonval))
Bugs fixed
- Remove the non-null assertion on `IDebugger.ISources` [10976](https://github.com/jupyterlab/jupyterlab/pull/10976) ([fcollonval](https://github.com/fcollonval))
- Protect against undefined delegated label [10972](https://github.com/jupyterlab/jupyterlab/pull/10972) ([fcollonval](https://github.com/fcollonval))
- ForwardPort PR 10898 on master: Render placeholder at correct index [10959](https://github.com/jupyterlab/jupyterlab/pull/10959) ([echarles](https://github.com/echarles))
- Fix lack of translation of part of "Saving completed" and friends [10958](https://github.com/jupyterlab/jupyterlab/pull/10958) ([krassowski](https://github.com/krassowski))
- Fix browser tab name [10952](https://github.com/jupyterlab/jupyterlab/pull/10952) ([tejasmorkar](https://github.com/tejasmorkar))
- Simplify IRankedMenu interface [10943](https://github.com/jupyterlab/jupyterlab/pull/10943) ([fcollonval](https://github.com/fcollonval))
- Add "menu" context for translation of menu labels [10932](https://github.com/jupyterlab/jupyterlab/pull/10932) ([krassowski](https://github.com/krassowski))
- Add undoManager to inserted cells [10899](https://github.com/jupyterlab/jupyterlab/pull/10899) ([hbcarlos](https://github.com/hbcarlos))
Maintenance and upkeep improvements
- Update to lerna 4 [10983](https://github.com/jupyterlab/jupyterlab/pull/10983) ([jtpio](https://github.com/jtpio))
- Galata: Update reference screenshots [10982](https://github.com/jupyterlab/jupyterlab/pull/10982) ([jtpio](https://github.com/jtpio))
- Improve Galata documentation and setup [10980](https://github.com/jupyterlab/jupyterlab/pull/10980) ([fcollonval](https://github.com/fcollonval))
- Clarify usage of mock in debugger test [10979](https://github.com/jupyterlab/jupyterlab/pull/10979) ([fcollonval](https://github.com/fcollonval))
- Restore test for kernel that does not support debugger [10973](https://github.com/jupyterlab/jupyterlab/pull/10973) ([fcollonval](https://github.com/fcollonval))
- Chore: fix typo in comments [10953](https://github.com/jupyterlab/jupyterlab/pull/10953) ([agoose77](https://github.com/agoose77))
- Bump major Galata version [10951](https://github.com/jupyterlab/jupyterlab/pull/10951) ([fcollonval](https://github.com/fcollonval))
- More robust UI tests [10950](https://github.com/jupyterlab/jupyterlab/pull/10950) ([fcollonval](https://github.com/fcollonval))
- More Publish Integrity [10937](https://github.com/jupyterlab/jupyterlab/pull/10937) ([afshin](https://github.com/afshin))
- Add Galata in JupyterLab [10796](https://github.com/jupyterlab/jupyterlab/pull/10796) ([fcollonval](https://github.com/fcollonval))
Documentation improvements
- Improve Galata documentation and setup [10980](https://github.com/jupyterlab/jupyterlab/pull/10980) ([fcollonval](https://github.com/fcollonval))
- Add process for adding a language [10961](https://github.com/jupyterlab/jupyterlab/pull/10961) ([fcollonval](https://github.com/fcollonval))
- Improve release notes for 3.1 [10954](https://github.com/jupyterlab/jupyterlab/pull/10954) ([krassowski](https://github.com/krassowski))
- Fix formatting of a link in the changelog [10945](https://github.com/jupyterlab/jupyterlab/pull/10945) ([jtpio](https://github.com/jtpio))
API and Breaking Changes
- Add debugger variable renderer based on mime type [10299](https://github.com/jupyterlab/jupyterlab/pull/10299) ([fcollonval](https://github.com/fcollonval))
Contributors to this release
([GitHub contributors page for this release](https://github.com/jupyterlab/jupyterlab/graphs/contributors?from=2021-08-25&to=2021-09-01&type=c))
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