v2.3.4

This is a hotfix update, cherry picking some important fixes from the last 2.4.0-beta.2 nightly release.

Cherry picks:

• Save files in different thread (#883)
• Fix delete key not working in markdown mode
• Fix export to multipage PDF leads to empty pages except the current one (#878)
• Fix undo/redo not working correctly and freezing the app
• Big translation updates

Read more here: https://linwood.dev/butterfly/2.3.4