Proposal for Spanish translation and feature request: Import/Export for plain text (.txt)

[laramaceo]

Hello StackEdit team,

I am an enthusiastic user of your tool and I would like to actively contribute to the project in the following ways:

UI Translation: I would like to translate the user interface into Spanish to make it more accessible. Could you please provide the steps to follow or let me know if there is a specific resource file (e.g., .json) that I should work on?

Feature Request (Import/Export .txt): I would like to suggest adding an option for direct export and import of plain text (.txt) files. This would allow users to work more flexibly with simple text files alongside the current Markdown options.

I look forward to your guidance so I can start contributing to the translation. Thank you for your great work!